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

Read CommandsAll read commands are generated by the program in the System/7 processor and sent to thearea station by the 2790 Control.Read: This code (hexadecimal 06) is sent after an area station has captured an any-addressframe and the area station has returned a read request response. The code puts the areastation adapter in data mode. The only valid response is read command acknowledge.Read Null: This code (hexadecimal 02) specifies that the frame is available for any typeof read request. This code should be generated by the program when no other commandis to be transmitted. Four valid responses are: read null acknowledge, read request, readdata request, and read end request.Read Data: This code (hexadecimal OA) is sent when a read data request response isreceived. The code causes the area station adapter to send the data byte again, so that avalidity check can be performed, and also releases the area station adapter to preparefor the next character. The only valid response is read data acknowledge.Read End: This code (hexadecimal OE) is sent either as a result of receiving a read endrequest from the area station adapter or as a result of detecting an error that requires 'the operation to be terminated. This command removes the area station adapter from datamode, thus causing the operation in progress to be terminated in the area station adapter.The area station refers to the data byte to determine which indicator light to turn on.The only valid response to this command is read end acknowledge. When the command issent to an area station local I/O adapter, the data byte contains an operator guidancecharacter. (Refer to the manual IBM 2790 Data Communication System ComponentDescription, Order No. GA27-3015, for a description of the operator guidance functions.)Read ResponsesAll read responses are generated by the area station and sent back to the 2790 Control.Read Request: This code (hexadecimal 12) is a response to a read null command when thearea station captures an any-address frame to initiate a read operation. The code indicatesthat the area station wants to transfer information to the 2790 Control.Read Command Acknowledge: This code (hexadecimal 46) is a response to a read command.The response indicates that the area station has received the read command and will startto read its data source (for example, a badge or a data entry unit).Read Data Request: This code (hexadecimal 62) is a response to a read null command ifthe area station adapter has a data byte to send to the 2790 Control.Read Data Acknowledge: This code (hexadecimal 6A) is a response to a read data command.The response indicates that the area station has executed the command. The area stationresponse digit is the same as in read data request response. The controlling program shouldcheck the data byte received for validity against the one received earlier with the readdata request.Read End Request: This code (hexadecimal 72) is a response to a read null command ifthe area station adapter has determined either that the data transfer has come to a normalcompletion or that an error has been detected. The status of the operation is transmittedin the data byte. An all-zero status designates a normal end.13-32 GA34-0003