Attention Interrupt Processing Routine

The entry conditions for the Attention Interrupt Processing exit routine vary for ASCII-type links or TCPASCII-type links.

For ASCII-type links, an attention interrupt is generated each time RSCS sends a data buffer. RSCS performs a Read Modified operation each time it receives an attention interrupt. This is required by the 7171 ASCII Device Attachment Control Unit to obtain the Attention Identifier (AID) byte. A null AID (X'E8') is usually returned. If the ASCII device has a keyboard, the attention generating keys (ENTER, PF key, or PA) can change the value of the AID. The exit routine can examine the AID byte and optionally pass a RSCS command back to the link driver for execution.

A TCPASCII-type link does not receive a single AID character. Rather, the exit is passed all data received from the terminal server as it arrives on the link.

If your routine passes a command to RSCS for execution, it must use the workstation operator form of the command. The length and address of the command are returned in registers 0 and 1. Setting register 0 to zero means that no command is to be processed and the default PF key commands are to be ignored. The only way to have RSCS use the default PF key commands is not to code an attention interrupt processing exit routine. A command length that is negative or exceeds 80 bytes terminates the link with user ABEND 012.