IBM System/7 Functional Characteristics - All about the IBM 1130 ...

Read End Acknowledge: This code (hexadecimal 3E) is a response to a read end command.The response indicates that the area station adapter will terminate the operation accordingto the status in the data byte. The transaction is completed when the code is receivedby the 2790 Control. The program should check the data byte received (ending status) forvalidity against the one transmitted earlier with the read end command.Read Null Acknowledge: This code (hexadecimal 42) is a response to a read null commandif no action is presently required by the area station adapter and the area station isin data mode.Write CommandsAll write commands are generated by the program in the System/7 processor and sent to thearea stations by the 2790 Control.Write: This code (hexadecimal 05) initiates a write operation and puts the area stationadapter in data mode. The only valid response is write command acknowledge. If the areastation adapter cannot execute this command, it will make an end request when it receivesthe next command, a write null command. If a write command is sent to an area stationlocal I/O adapter and the adapter is busy, the area station will return a data bytecontaining hexadecimal 80. The command should be sent repeatedly until a write commandacknowledge response is received.Write Null: This code (hexadecimal 01) specifies that the frame is available for anytype of write request from the device that is addressed. There are three valid responses:write null acknowledge, write data request, and write end request.Write Data: This code (hexadecimal 09) is sent to an area station when a write datarequest is received. This command is accompanied by a data byte, and the only validresponse is write data acknowledge.Write End: This code (hexadecimal OD) is normally sent if a write data request responseis received and there is no data left to be transmitted. The command can also be sent asa result of a program detected error, or as a result of a write end request response bythe area station adapter after it detects an abnormal condition. The data byte with thewrite end command is used as a status field, with all 0's representing normal end. Theonly valid response is a write end acknowledge.Write ResponsesAll write responses are generated by the area station and sent back to the 2790 Control.Write Data Request: This code (hexadecimal 51) is a response to a write null commandif the area station adapter is ready to receive a data byte.Write Data Acknowledge: This code (hexadecimal 69) is a response to a write datacommand, and indicates that the area station has received the data byte. The program shouldcheck the data byte received for validity against the one transmitted earlier with thewrite data command.Write. End Request: This code (hexadecimal 71) is a response to a write null command ifthe area station adapter has detected an error or an unusual condition. The status is alsosent in the data byte.Write End Acknowledge: This code (hexadecimal 3D) is a response to a write end command.This response indicates that the area station adapter will terminate the operation accordingto the status in the data byte as modified by the area station adapter. An all-zero statusrepresents normal end. The received status byte should be checked by the program forvalidity against the transmitted status byte.