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

1,114plilloi 1110 1111 1111.11 VI P inRead ISW0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA00001XXX0100000000110011000000001111 11 11 1111 III 11111 111110 8-F 4 0 3 3 0 0This command reads the ISW into the register specified by the R field, or the accumulatorif R= 000. It does not cause an interruption.Interrupt Status Word (ISW)Bits in the ISW are set on to indicate the operating status of the BSCA and to notify thesystem of errors detected. Execution of the read ISW command, after the BSCA recognizesthat its request has been accepted by the processor, resets the ISW. The ISW is alsoreset by system reset, or the first new selection of the BSCA (not read ISW) after itsinterruption request has been accepted by the processor.A description of each bit in the BSCA ISW follows.Bits Meaning0* Attention. This bit is set when the ring indicator line from the modem is active.It is not an error condition.1* Command reject. This bit is set on by any of the following conditions:1. The data set ready line is not active when either a transmit or receiveoperation is initiated.2. A transmit operation is attempted while in receive mode or a receiveoperation is attempted while in transmit mode.3. An allow transparent control operation is attempted while not in transparenttext mode.4. An odd number of bits (parity error) is word 3 of the DCB.5. No function is requested in word 3 of the DCB.6. On a multipoint network, a transmit operation is attempted beforethe status is selected.2* Overrun. During a transmit operation, overrun occurs if no data is presentedfor transmission and synchronous idle control characters have been insertedfor 3 seconds. During a receive operation, overrun occurs if the word counthas been decremented to zero, no COD character was received, and anotherreceive operation was not initiated by the time the receive buffer was filled.In either case, the BSCA interrupts with this bit set on the next time itbecomes busy.3* Timeout. Occurs under any of the following conditions:1. Character phase (SYN SYN) is not established within 3 seconds afteracceptance of a receive data operation. This is under program controland is effective only if bit 11 is set on in word 3 of the current DCB.2. Continuous synchronization pattern, or transparent synchronizationidle in transparent mode, is received for 3 seconds.3. While receiving data, no synchronization pattern or no transparentsynchronization idle is received for 3 seconds.4. Clear to send is not returned from the modem within 3 seconds afterrequest to send is presented.5. Data set ready is not returned from the modem within 3 seconds afteran enable with timer operation is begun.A