There is disclosed a method capable of maintaining and administering remotely a switchboard at each site with a computer in the remote switching operation center which gets through a public switching telephone network (PSTN). The improvement allows that a loading file and a mail file are mutually transmitted between a computer in the remote switching operation center and a switchboard at each site, and that a data conversation function is performed between a computer in the remote switching operation center and a maintenance and administration (M & A) terminal installed in the switchboard at each site.

In a general-purpose subscriber unit a data communication method provides management and control functions to allow communication between one of a plurality of software applications and a selected communication device, such as a radio frequency modem. Messages received by the modem may be routed and stored for designated ones of said applications, even if they are not currently active. Likewise, an application operating in background mode may generate messages which are stored, routed, and transmitted through the modem.

A system is shown for interfacing between a work station or intelligent terminal device and a number of maintainable telecommunication systems. This system provides for interfacing between an intelligent CRT terminal and up to 26 remotely located maintenance processor units. This system provides the CRT attendant or crafts person with the ability to trouble-shoot or perform diagnostic testing upon a maintenance processor unit which is remotely located. In addition, the work station or intelligent terminal may be remotely located from the interface circuitry. This system establishes a connection between the work station or intelligent terminal and a particular maintenance processor unit. Once that connection is established, the maintenance processor unit of that telecommunications system reports diagnostic and trouble-shooting type information. This system also provides for manual reset and self test capabilities. This system provides for a variable BAUD rate which may be preprogrammed into a microcontroller device.

An input circuit for an input/output device adapted for use in a computer system in which a command includes information indicating an application program which initiated the command, the input circuit including a first-in first-out (FIFO) buffer circuit having a plurality of stages, each stage providing storage for commands from application programs including both data and an address for the data, circuitry for determining from a command an application program which has initiated a command, and circuitry for assuring that commands from only one application program reside in the FIFO buffer at any time.