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Claims  |
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What is claimed is:
1. A boundary scan circuit cell suitable for use in a boundary scan test
serial scan chain for boundary scan testing of an integrated circuit
component having a bidirectional pin, said boundary scan circuit cell
comprising:
a bidirectional input-output terminal;
a data scan-in line;
a data scan-out line;
a scan clock line;
a data register shift line;
first and second data registers serially connected between said scan-in and
scan-out lines for shifting binary data from said scan-in to said scan-out
lines sequentially through said first and second registers in response to
clock pulses received from said scan clock line;
an output driver coupled to one of said first and second registers and to
said input-output terminal for selectively driving said input-output
terminal in accordance with binary data received from said one register in
response to an enable signal;
a first multiplexer connected to said one register, said input-output
terminal and said data scan-in line, for selectively transmitting either
said serially shifted binary data from said scan-in line or a state of
said input-output terminal to said one register in accordance with signals
received on said data register shift line;
a control circuit coupled to the other of said first and second registers
and to said output driver for selectively delivering said enable signal to
said output driver in accordance with binary data received from said other
register; and
a second multiplexer connected to said other register and said one
register, for selectively transmitting either serially shifted contents of
said one register or contents of said other register to said other
register in accordance with said signals received on said data register
shift line.
2. A test fixture for boundary scan testing an integrated circuit or
circuit board unit under test, comprising:
connection terminals for connection to said unit under test;
a boundary scan signal bus;
a boundary scan driver/sensor integrated circuit, comprising:
a plurality of boundary scan circuit cells as defined in claim 1;
each input-output terminal corresponding to a respective one of said
connection terminals, and the data scan-in and data scan-out lines of the
plurality of circuit cells being serially connected in a single serial
scan chain that enables said serially shifted binary data to be shifted in
a single data stream, sequentially through the plurality of circuit cells;
a test data input pin coupled to said boundary scan signal bus;
a test data output pin coupled to said boundary scan signal bus;
a boundary scan test access port circuit coupled to control receipt of the
single data stream from the test data input pin to the circuit cells and
delivery of the single data stream from the circuit cells to the test data
output pin.
3. The circuit of claim 1, further comprising a data register hold line; a
first latch connected to receive and latch output from said one register
and deliver said latched one register output to said output driver; and a
second latch connected to receive and latch output from said other
register and deliver said latched other register output as said enable
signal to said output driver; said latching operation being under control
of signals received from said data register hold line.
4. The circuit of claim 3, further comprising a test mode line, and wherein
said control circuit comprises a binary signal logic gate connected
between said second latch output and said enable input of said driver.
5. The circuit of claim 4, wherein said gate comprises a NAND gate.
6. The circuit of claim 5, further comprising a buffer connected between
said input-output terminal and said first multiplexer.
7. The circuit of claim 6, wherein said registers comprise flip-flop
circuits.
8. A boundary scan driver/sensor integrated circuit, comprising:
a plurality of input-output pins;
a plurality of boundary scan circuit cells as defined in claim 1; each
input-output terminal corresponding to a respective one of said
input-output pins, and the data scan-in and data scan-out lines of the
plurality of circuit cells being serially connected in a single serial
scan chain that enables said serially shifted binary data to be shifted in
a single data stream, sequentially through the plurality of circuit cells;
a test data input pin;
a test data output pin;
a boundary scan test access port circuit coupled to control receipt of the
single data stream from the test data input pin to the circuit cells and
delivery of the single data stream from the circuit cells to the test data
output pin.
9. The boundary scan driver/sensor integrated circuit of claim 8, wherein
said test access port circuit comprises circuitry compatible with IEEE
1149.1 JTAG bus standard.
10. The boundary scan driver/sensor integrated circuit of claim 8, further
comprising a test data output circuit coupled between the test data output
pin and a last of the circuit cells in the serial scan chain; and an
instruction register circuit coupled to the test data input pin, test
access port circuit, test data output port circuit and circuit cells, and
programmable to control functions of the circuit cells and the test data
output circuit.
11. The boundary scan driver/sensor integrated circuit of claim 10, further
comprising a bypass register coupled to the test data input pin and the
test data output port circuit, and operable to selectively pass data from
the test data input pin to the test data output port circuit, bypassing
the circuit cell serial scan chain.
12. The boundary scan driver/sensor integrated circuit of claim 10, wherein
said instruction register circuit further comprises:
first and second memories serially coupled for selectively receiving data
on a serial data input;
first and second input multiplexers operable to selectively load serial
data or a specified default pattern into said first and second memories;
and
third and fourth memories coupled to said first and second memories,
respectively, and operable to selectively store instruction bits for
transmission to other logic circuitry.
13. The boundary scan driver/sensor integrated circuit of claim 8, wherein
in each circuit cell said multiplexer is connected to said first register;
said first register is a first memory for data storage, and said second
register is a second memory for data storage; and said each circuit cell
further comprises a third memory for data storage coupled to said first
memory and operable to selectively transmit stored data from said first
memory to said associated output driver, and a fourth memory coupled to
said third memory and operable to selectively transmit stored data from
said second memory to said associated output driver for selectively
delivering said enabling signal to said associated output driver.
14. The boundary scan driver/sensor integrated circuit of claim 13, wherein
said multiplexer comprises a first multiplexer, and each circuit cell
further comprises a second multiplexer connected to said second memory and
to an output of said second memory, for selectively transmitting either
said serially shifted binary data or said contents of said second memory
to said second memory responsive to said signals received on said data
register shift line.
15. The boundary scan driver/sensor integrated circuit of claim 14, wherein
said circuit cells are connected from a lowest to a highest order circuit
cell in said serial scan chain; with said first multiplexer of a lowest
ordered one of said circuit cells being coupled to selectively receive
said single data stream input from said test data input pin; with said
first multiplexers of intermediate ordered ones of said circuit cells
being respectively coupled to selectively receive said single data stream
input from said second memory of a next lower ordered one of said circuit
cells; and with said second memory of a highest one of said circuit cells
being coupled to transmit output to said test data output pin.
16. A circuit board having boundary scan testability features, comprising:
a first integrated circuit having external connection pins which do not
have on-board associated boundary scan testing circuitry;
a boundary scan signal bus; and
a boundary scan driver/sensor integrated circuit as defined in claim 8
wherein said test data input pin and said test data output pin are coupled
to said boundary scan signal bus.
17. The circuit board of claim 16, wherein said boundary scan signal bus
meets the requirements of the IEEE 1149.1 JTAG bus standard.
18. The circuit board of claim 16, wherein said boundary scan test access
port circuit comprises circuitry compatible with the IEEE 1149.1 JTAG bus
standard.
19. The circuit board of claim 16, further comprising a second integrated
circuit having on-board associated boundary scan testing circuitry
connected in another serial scan chain; said on-board scan testing
circuitry and said boundary scan driver/sensor integrated circuit being
coupled, so that said single data stream can be shifted sequentially
through both said single serial scan chain and said another serial scan
chain.
20. The circuit board of claim 19, wherein said boundary scan driver/sensor
integrated circuit further comprises a bypass register operable to
selectively transmit boundary scan test data from said boundary scan
signal bus, through said bypass register, to said another serial scan
chain, without passing through said single scan chain.
21. A boundary scan circuit suitable for use in a boundary scan test of an
integrated circuit component having a bidirectional pin, said boundary
scan circuit comprising:
a bidirectional input-output terminal;
a data scan-in line;
a data scan-out line;
a scan clock line;
a data register shift line;
first and second data registers serially connected between said scan-in and
scan-out lines for shifting binary data from said scan-in to said scan-out
lines sequentially through said first and second data registers in
response to clock pulses received from said scan clock line;
an output data latch connected to said first register;
an output driver coupled to said output data latch for selectively driving
said input-output terminal in accordance with binary data latched in said
output data latch received in response to an enable signal;
a first multiplexer connected to said first register, said input-output
terminal and said data scan-in line, for selectively transmitting either
said serially shifted binary data from said scan-in line or a state of
said input-output terminal to said first register;
a control latch circuit coupled to said second data register and to said
output driver for selectively delivering said enable signal to said output
driver in accordance with binary data latched in said control latch; and
a second multiplexer connected to said second register and said first
register, for selectively transmitting either data from said first
register or data from said second register to said second register.
22. A boundary scan driver/sensor integrated circuit, comprising:
a plurality of input-output pins;
a plurality of input buffers respectively coupled to said input-output
pins;
a plurality of output buffers respectively coupled to said input-output
pins;
a plurality of input-output pin control circuits each coupled to respective
ones of said input and output buffers and each serially coupled to the
adjacent input-output control circuits to form a serial scan path, each of
said input-output pin control circuits comprising:
(a) data storage circuitry comprising a first multiplexer coupled to
selectively receive input data from the respective input buffer, and
alternatively to receive serial data in said serial scan path; a first
memory coupled to said first multiplexer for capturing said first
multiplexer received data; and a second memory coupled to said first
memory and operable, when the respective output buffer is enabled, to
selectively transmit a test bit of said first memory captured data to the
respective output buffer while said first memory is receiving data; and
(b) control storage circuitry comprising a second multiplexer operable to
receive said first memory captured data in said serial scan path from said
first memory of said data storage circuitry; a third memory coupled to
said second multiplexer for capturing said second multiplexer received
data and operable to output said third memory captured data in said serial
scan path, and a fourth memory coupled to said third memory and operable
to transmit a control bit of said third memory captured data to control
enabling of the respective output buffer while said third memory is
receiving or transmitting said second multiplexer received data;
a boundary scan test access port circuit configured to be coupled to an
external serial test bus;
a test data output circuit;
an instruction register circuit coupled to the boundary scan test access
port circuit and programmable to control the functions of the input-output
pin control circuits and the test data output circuit; and
operable so that the boundary scan driver/sensor circuit selectively
asserts and captures data on the input-output pins responsive to
instructions and data supplied on the serial test bus;
wherein said instruction register circuit further comprises:
fifth and sixth memories serially coupled for selectively receiving data on
a serial data input;
first and second input multiplexers operable to selectively load serial
data or a specified default pattern into said fifth and sixth memories;
and
seventh and eighth memories coupled to said fifth and sixth memories,
respectively, and operable to selectively store instruction bits for
transmission to other logic circuitry. |
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Claims |
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Description |
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(C) Copyright, *M* Texas Instruments Incorporated 1991. A portion of the
disclosure of this patent document contains material which is subject to
copyright and mask work protection. The copyright and mask work owner has
no objection to the facsimile reproduction by anyone of the patent
document or the patent disclosure, as it appears in the Patent and
Trademark Office patent file or records, but otherwise reserves all
copyright and mask work rights whatsoever.
FIELD OF THE INVENTION
This invention relates generally to integrated circuits utilizing boundary
scan testability technology and applications of boundary scan circuits and
techniques in applications such as circuit board design using high density
technologies like surface mount technology (SMT), application specific
integrated circuits (ASICs), programmable integrated circuits and systems.
BACKGROUND OF THE INVENTION
It is often desirable to provide improved accessibility to specific areas
of an integrated circuit or a group of integrated circuits installed in a
surface mount technology (SMT) or other high density environment (TAB,
PCB) that allows the user to test and verify proper operation of a
particular IC or path without any modification of the hardware or
additional physical connections to the circuits or to the system the
circuits reside in. The test access hardware should not affect the normal
operation of the circuits or create additional delays or performance
problems, and should be done nonintrusively so that the individual
integrated circuits and the system can be tested while installed in an
operational environment. The need for this kind of testability access led
to the development of boundary scan techniques which allow access to the
pins of the integrated circuits without intrusive test hardware. The need
to test integrated circuits manufactured by different vendors in a system
environment further led to the development of a standard testability bus
for boundary scan applications, the JTAG (Joint Test Action Group)
standard bus. The JTAG bus is now governed by IEEE standard 1149.1.
A designer who wishes to build boundary scan testing into a circuit board,
integrated circuit or system and use the JTAG bus must first implement the
boundary scan path and configure it for the particular application or
system. This task becomes particularly difficult when the designer intends
to use memories or other off-the-shelf components which are not JTAG
compatible. The high cost of designing hardware or a custom integrated
circuit for a particular application, coupled with the amount of time
required to design, test and fabricate such hardware or customized
integrated circuits creates a need for a general purpose, universal,
programmable integrated circuit device which can be used to implement and
test boundary scan paths using the JTAG bus for any application.
Without limiting the scope of the invention, its background is described in
connection with boundary scan techniques used to test and communicate with
integrated circuit devices (ICs) not having built in boundary scan
capabilities. Although the particular embodiment presupposes the use of
the JTAG standard bus, alternative communication arrangements can be used,
as will be obvious to one experienced in the art.
Heretofore, in this field, various boundary scan techniques have been used
by system designers. However, each designer has had to implement a scan
bus specifically designed for each application. The time and cost of
designing, testing and manufacturing hardware or custom integrated
circuits for each system is prohibitive. Further, the use of several
different systems in one operating environment, each system having a
different boundary scan methodology, results in reduced capability and
creates a need for additional translation hardware or bus couplers which
require additional design and test time and may reduce overall system
performance.
SUMMARY OF THE INVENTION
Generally, and in one form of the invention, a programmable integrated
circuit consisting of a plurality of input/output buffers each coupled to
an I/O pin control circuit, the I/O pin control circuits being serially
coupled to provide scan path access to the entire plurality of I/O pin
control circuits and pins, a bypass circuit to provide a method for
communicating to other programmable integrated circuits serially coupled
without affecting the normal non-test operations in progress, an
instruction decoding block which receives serial data and commands from a
JTAG bus, decodes a set of instructions and in response controls the
input/output buffers and bypass logic, and a JTAG Test Access Port circuit
which couples the integrated circuit to a standard JTAG bus is described.
Each I/O pin (64 in the described implementation) provided by the device is
independently programmable, so that the device can be used in test
applications to drive and sense test vector data to or from the device
under test. Each I/O pin has two associated boundary scan bits, to allow
the output driver to be configured as either enabled or disabled and the
logic level asserted to be either a logic 1 or logic 0 for each pin. A
reset state where all drivers are configured in tri-state mode is provided
to prevent clashes with the unit under test at power up or during initial
programming.
The device architecture may also be embedded in application logic to
provide testability functions in areas of otherwise low JTAG observability
to improve testability.
Further embodiments disclosed herein involve using the boundary scan
integrated circuit as part of a test fixture for testing integrated
circuits or circuit boards. Multiple universal boundary scan driver/sensor
ICs are serially interconnected until the required number of I/O pins is
provided for connection to the device under test. This technique
advantageously provides a method for rapidly constructing a test fixture
for any device which is to be tested without additional hardware design or
manufacturing overhead.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a block diagram of the Boundary Scan Driver/Sensor Device;
FIG. 2 is a diagram of the I/O pin control circuitry;
FIG. 3 is a diagram of the bypass circuitry;
FIG. 4 is a diagram of the instruction decode circuitry;
FIG. 5 is a diagram of the TDO Select and Resync circuitry;
FIG. 6 is a diagram of the JTAG Test Access Port (TAP) circuitry; and
FIG. 7 is a block diagram of an application of the driver/sensor IC in a
device test fixture.
Corresponding numerals and symbols in the different figures refer to
corresponding parts, unless otherwise indicated.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In FIG. 1, a diagram of an integrated circuit containing the boundary scan
sensor/driver circuitry 1 is depicted. A plurality of I/O control circuits
3 is shown, each serially coupled to its nearest neighbors and each
coupled to an I/O buffer 5 consisting of an input buffer, an output buffer
with an enable line, and a pad. The output of the scan path leaves the
highest ordered I/O control block (here, there are 64 by way of example,
enumerated from 0 to 63) and is coupled to the Test Data Output (TDO)
Select and Resync circuitry 11.
The JTAG bus is coupled to the JTAG Test Access Port (TAP) circuitry 13.
The test data input signal from the JTAG bus, TDI, is coupled to the
lowest ordered I/O control circuit 3, the Bypass circuitry 7, and the
Instruction register circuitry 9.
In operation, the JTAG bus sends command and data messages by handshaking
with the Boundary Scan Driver/Sensor IC on the TMS, TRST.sub.-- and TCK
lines. Commands are sent as serial data on the TDI line and shifted into
the Instruction register 9 for decoding. The reader is referred to the
JTAG Bus Specification, IEEE standard 1149.1, for details and timing of
the transmission of commands and data on the JTAG bus.
Once a command is shifted into the Instruction block 9 and decoded, the
Boundary Scan Sensor IC executes the instruction to shift in data from the
JTAG bus to the I/O control circuits 3, shift out captured data onto the
JTAG bus by means of the TDO Select and Resync circuit 11, capture data
present on the I/O lines into the I/O control circuits 3, or drive data
onto the I/O lines by means of the I/O buffers 5. Although many
enhancements are possible within the scope of this invention which will be
obvious to the reader familiar with the art, these four operations are
described in detail later herein by way of example.
FIG. 2 depicts the internal circuitry of the I/O control blocks and the I/O
buffer circuitry. Each I/O control block consists of two flip-flop
registers and two latches, the data register 15 and data latch 25 and the
control register 17 and control latch 23. Additionally, the data and
control registers each have an input mux, the data input mux 19 and the
control input mux 21. The output of the control latch 23 is gated with the
input signal TESTMODE at NAND gate 31, so that the output driver 27 is
only enabled when TESTMODE is true and the output of the control latch 23
is true. The output driver 27 is coupled to the I/O terminal pad 29, and
the input driver 33 provides a path for data supplied by the device under
test back into the scan path via the data input mux 19.
The scan path contains two bits per I/O control block, one for data and one
for control. To program a particular pin, the user determines for each
test vector whether the pin is to be used as an output or an input, and
for an output pin what logic value is to be asserted. These two bits are
then shifted into the I/O control block data and control registers 15 and
17 respectively, by use of the DRSHIFT and SCANCK inputs provided by the
Test Access Port circuitry in response to commands on the JTAG bus. The
TD(N) scan input line is used to couple each I/O control block to the
previous one in the scan path, the output of the data register 15 is
coupled through the control input multiplexer 21 into the control register
17 and the output of control register 17 is coupled to the TD(N+1) scan
output for coupling to the TD(N) input to the next adjacent I/O control
block. Once the registers for each I/O control block have been configured
properly by means of the scanning operation, the DRHOLD line will become
active and those I/O control blocks configured as outputs will supply data
from the output latch 25 to the output driver 27, and the control line
signal will be provided by control latch 23, through NAND gate 31 to the
output enable of the output driver 27. After the test vector has been
asserted the DRHOLD line can be used to latch the control bit for the
drivers while the next test vector is being scanned into the boundary scan
path.
Data may also be captured as input data from the device under test through
the input buffer 33, the input multiplexer 19 and into the data register
15 responsive to the SCANCK input. The scanning operation described above
is then used to transmit the data captured onto the JTAG bus by means of
the TDO Select and Resync block 11 and the TDO output pin (see FIG. 1).
FIG. 3 depicts the internal logic used in the JTAG bus required Bypass
circuitry 7. The Bypass circuitry 7 consists of a 2-to-1 input multiplexer
35 coupled to a register 37, the output of which is coupled to a 2-to-1
output multiplexer 39.
In operation, the DRSHIFT line controls whether the TDI input is passed
into the register 37 through the input multiplexer 35, and the SCANSEL
input controls whether the registered data is passed from the register 37
onto the output signal BOR through the output multiplexer 39. When the
boundary scan path through the I/O control blocks is in use, the SCANSEL
input selects the TD(64) input for the output mux 39, when the Bypass
circuit is active the SCANSEL input selects the output of register 37. The
BOR signal is coupled to the TDO Select and Resync logic (See FIG. 1) for
sourcing the TDO output pin. In this way, a Boundary Scan Driver/Sensor
which is not to be used in the current JTAG operation may be bypassed, and
the data coming in is shifted through register 37 and out onto the TDO pin
for use by devices further along in the JTAG chain.
FIG. 4 depicts the Instruction Register 9 internal circuitry. The
Instruction Register in the described preferred embodiment consists of two
registers, 43 and 47, serially linked such that the bits supplied by the
JTAG data line may be scanned in, two latches 49 and 51 such that the bits
scanned in may be passed out as the TESTMODE and SCANSEL control lines,
and two input multiplexers 41 and 45 such that the register can be loaded
with the default instruction or the incoming instruction can be scanned
in. Output IR(0) is coupled to the TDO Select and Resync circuit 11 such
that the contents of the register can be read by means of scanning the
bits out onto the TDO pin (See FIG. 1).
In operation, the JTAG Test Access Port circuitry 13 controls control lines
IRHOLDZ and IRSHIFTZ when the Instruction Register 9 is programmed and
used. The input multiplexers 41 and 45 respond to the IRSHIFTZ to enable
the TDI serial data to be shifted into the Instruction Register flip-flops
41 and 45. The IRHOLDZ input is asserted to latch the last active
instruction in latches 49 and 45. Once loaded, the instruction may be
enabled by de-asserting the IRHOLDZ input to allow the new instruction in
the registers to be pass through the latches 49 and 51. The new
instruction data will then appear at the SCANSEL and TESTMODE outputs
which control the logic in the I/O control blocks described above.
Because the Instruction register 9 is two bits wide, it will be readily
apparent that there are four different instructions available based on the
value of the IR bits 1 and 0. These instructions are EXTEST, (`00`),
SAMPLE/PRELOAD (`01`), ASSERT & BYPASS (`10`), and BYPASS (`11`). Each
instruction will be described below (the reader should refer to FIG. 2 for
details on the circuitry in the I/O Control block, FIG. 3 for the details
on the circuitry in the Bypass block, and FIG. 5 for the details of the
TDO Select and Resync block).
The EXTEST instruction results in both the SCANSEL and TESTMODE outputs
being a logic 1. The SCANSEL output enables the SCANCK signal to the I/O
Control blocks, so that the data registers inside the I/O Control Blocks
will receive a clock and first sample the input signals and then shift out
the sampled values while shifting in a new set of assertion and control
bits. The TESTMODE signal, when 1, enables the I/O Control output buffers
such that the pins of the device will be driven (if the corresponding
output enable bit is also 1).
The SAMPLE/PRELOAD command results in the TESTMODE signal being 0, while
the SCANSEL signal is a 1. The output buffers in the I/O Control blocks
will again be tristated, while the SCANCK input to the registers in the
I/O Control blocks will be enabled, so that the incoming data may be
sampled, or the scan path through the I/O Control blocks may be operated
to preload the scan path with the next test vector.
The ASSERT & BYPASS command results in the TESTMODE signal being a logic 1,
while the SCANSEL signal is a logic 0. The TESTMODE signal will enable the
I/O Control blocks which are configured as output enabled drivers to
assert the data onto the I/O pins, while the SCANSEL signal value of a
logic zero will prevent the registers in the I/O Control blocks from being
clocked, so that the values stored there will remain constant. The SCANSEL
signal also selects the output of the Bypass Register as the source for
the TDO block, so that if the DRSHIFTZ line becomes active during the
ASSERT & BYPASS command, the data on the TDO line will be the data
shifting through the Bypass register.
The BYPASS command results in the TESTMODE signal being a logic 0, and the
SCANSEL signal also being a logic 0. This results in the I/O Control
blocks being held at the previous state, as the SCANCK signal is disabled
and since the TESTMODE signal is low disabling the output buffers, the
outputs are tri-stated. The SCANSEL signal being low enables the output of
the Bypass register to appear on the TDO output pin. If a shift operation
is begun by the TAP block, the data shifted in on the TDI input will be
shifted out onto the TDO output, so that the part is not active in the
current JTAG transaction.
The STRAPZ input is asserted by the JTAG TAP logic in response to a reset
condition on the JTAG bus to provide the default command, BYPASS, at
reset.
FIG. 5 depicts the Test Data Output (TDO) Select and Resync block
circuitry. Input multiplexer 53 couples either the output signal from the
Bypass register, BOR, or the output signal from the Instruction register,
IR(0), to the register 55. Register 55 is clocked with the buffered signal
TCKZ, which resynchronizes the operation with the JTAG bus clock, TCK.
Output driver 57 is controlled by input TDOENAZ to assert the registered
bit onto the JTAG bus for transmission to other devices as signal TDO on
pad 59.
FIG. 6 depicts the internal circuitry of the JTAG Test Access Port (TAP)
block. The JTAG Test Access Port is a standard part of the Texas
Instrument ASIC library used for coupling a JTAG bus to an integrated
circuit. The Test Access Port is a state machine implementing the JTAG
protocol, and it supplies the control signals STRAPZ, TDOENAZ, SELECT,
IRSHIFTZ, IRCK, IRHOLDZ, DRSHIFTZ, DRCK, and DRHOLDZ to the logic blocks
described above. The Test Access Port standard cell is described in
Appendix D-2 of the Texas Instruments databook entitled "TSC500 Series,
1-um CMOS Standard Cells". This description is incorporated herein by
reference.
In Table 1, various configurations of the Boundary Scan Driver/Sensor IC in
different packaging and pinout configurations are described. Here, by way
of example, a total of 64 I/O control circuits in a single IC is assumed,
although larger configurations are possible without hardware modification
beyond required fanout buffering for clock and control lines. Many other
configurations are possible and within the scope of this invention, as
will be apparent to those skilled in the art. The configurations described
in Table 1 are merely illustrative and are not meant to limit the scope of
the invention.
For example, line 1 of Table 1 describes a 28 pin PDIP package having 18
I/O control block circuits and I/O pins, five pins dedicated to the JTAG
bus, two VCC pins and three Gnd pins.
TABLE 1
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Boundary Scan Driver/Sensor IC Configuration
PACKAGE PINS I/O JTAG VCC GND
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PDIP 28 18 5 2 3
PDIP 40 28 5 3 4
PLCC 28 18 5 2 3
PLCC 44 30 5 4 5
PLCC 68 50 5 5 8
PLCC 84 64 5 5 10
PQFP 80 62 5 5 8
PQFP 100 64 5 15 16
PPGA 100 64 5 15 16
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FIG. 7 depicts the use of the Boundary Scan Sensor/Driver IC's to implement
a test fixture of any arbitrary board, system or IC built without JTAG bus
capability. Test Control System 85 is a JTAG bus compatible controller
which allows the user to communicate with the Boundary Scan ICs 87 using
the JTAG bus. Unit under test 89 is the board, system or IC which is to be
tested.
In designing a circuit board using parts which do not have JTAG capability,
the designer may use as many of the Boundary Scan Sensor/Driver ICs as
needed to couple the signals to be tested to a JTAG bus by serially
interconnecting the parts into scan paths of the desired lengths as shown
in FIG. 7. The JTAG bus may then be used to test and observe the data
supplied by and used by these parts. The use of the Boundary Scan
Sensor/Driver IC makes it possible to advantageously design a circuit
board or system having advanced testability and observability while using
existing, non-testable ICs without additional hardware design.
FIG. 7 depicts the use of several Driver/Sensor ICs to implement a JTAG
test fixture for any unit for which testability is required, be it a
single IC or circuit board or system. The user can create the test fixture
simply by coupling multiple Driver/Sensor IC's together until a sufficient
number of I/O pins is available, connecting the Boundary Driver IC I/Os to
the Unit Under Test, and coupling the JTAG ports of the Boundary Scan
Sensor/Driver ICs in parallel on a JTAG bus coupled to the Test Control
System. This allows rapid design of a test fixture using JTAG without
additional hardware complexity or design required.
A few preferred embodiments have been described in detail hereinabove. It
is to be understood that the scope of the invention also comprehends
embodiments different from those described, yet within the scope of the
claims.
While this invention has been described with reference to illustrative
embodiments, this description is not intended to be construed in a
limiting sense. Various modifications and combinations of the illustrative
embodiments, as well as other embodiments of the invention, will be
apparent to persons skilled in the art upon reference to the description.
It is therefore intended that the appended claims encompass any such
modifications or embodiments.
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