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

Bit 15 in the R register can be set as follows:Bit 15 = 0 An interruption request is presented if an inactiveframe cycle is received (bytes 2 to 5 are sync characters).Bit 15 = 1 The input shift register shifts logical l's into theinput buffer register. When all positions in the registercontain l's, an interruption request is presented to theprocessor module. Since the 2790 Control is in diagnosticmode, this "forced" shifting checks the input circuitswithout using the output portion of the function.A read-address or read-control-and-data command would normally follow theset-input-buffer-control command when the interrupt is requested by the 2790 Control.Read /SW0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA00001 XXX 010000000011100000 XXXXXXi ill II II 1111 III 1 1 1 1 1 111110 8-F 4 0 3 8 0-3 XThis command stores the 16-bit interrupt status word (ISW) into the index register (R),or the accumulator if R=000.Interrupt Status Word (ISW): The 16 bits in the interrupt status word are set to indicateoperating status of the 2790 Control function and to detect errors that occur after awrite-control-and-data command is completed, but while the device is still busy. TheISW bits are reset on the first selection of the 2790 Control function after the interruptionrequest has been accepted by the processor module.Significant bits in the 2790 Control ISW and their meanings are:Significant Bits Meaning3 Frame parity error. One of the four bytes of an active framereceived in the input buffer had a parity error.4 No input detected. The 2790 Control input circuits did not receive aninput pulse from the loop within 1.024 ms.5 Diagnostic mode. The 2790 Control is in the diagnostic mode ofoperation. This is not an error.6 No sync bytes. A byte other than a sync byte was detected in bytes 5to 29 of a frame cycle. This is valid only when the 2790 Control is indiagnostic mode, and is not an error.7 Bypass mode. The 2790 Control function is in the bypass mode ofoperation. This is not an error.12 Device busy. The 2790 Control is transmitting an active frame andis waiting for the interrupt from the frame returning in the inputbuffer.13 Device end. The 2790 Control has completed the requested operation.13-44 GA34-0003