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

1111 11 I 111111111111WRead Initialize (DPC)0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA0 0 0 0 1 XX OO 1 0 0 0 0 0 0 1 1 0 • • **'XXXXXX1 I I i ii II 1 1 i 1 I I till! 1 1 1 1 I•••••••••,•■••• ••••■••■,,■' •■■•••,„...a..• •••••••■•■••••••••O 8-F 2 0 6 0 0-3 XThis command places the disk storage module in the read data mode of operation andsearches for the sector identifier specified by the control information word contained inthe index register (R), or the accumulator if R=000. The control information word has thefollowing format:O '2 1011 15F C T S1111Sector identifiers are read on the track previously specified and compared to the identifierspecified by the control information word. When the specified sector is found, thefirst four data words in the sector are read from the disk into the file data buffer and adata-service interruption request is presented to the processor. If the sector is not foundafter at least one complete revolution of the selected disk, the no-record-found bit (bit 5)is set in the interrupt status word and an interruption request is presented to theprocessor.Upon completion of a successful read initialize command, the disk storage module canaccept only a read data or terminate command. Read data mode is reset by either anend-of-sector or an any-error interruption request.Read Data (DPC)O 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA0 0 0 0 1 XXXO 1 0 0 0 0 0 0 0 0 0 1******XXXXXX1 1 1 1 II 11 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1••••••■••■,.■■ •■••••,,www."•■•••••■,,,■■■••• •■••••••,,..•••• ••■•••■,,■•■■■••O 8-F 4 0 1 0 0-3 XThis command transfers one 16-bit data word from the disk file data buffer to the indexregister (R), or the accumulator if R=000. The read data command is valid only after aread initialize command has placed the disk storage module in the read data mode of operationand read the first four data words from the disk.Data-service interruption requests occur at 40-microsecond intervals. Four read datacommands must empty the disk file data buffer within this interval to avoid a data overruncondition. If the data buffer is not emptied within 40 microseconds, the overrun errorbit (bit 2) is set in the interrupt status word and a device-end interruption is presented.Once the data buffer is emptied, the disk storage module is busy to any more read datacommands until the next data-service interruption request occurs.After 128 data words and the check character for the entire data field are successfullyread, the end-of-sector bit (bit 7) is set in the interrupt status word and an interruptionrequest is presented.