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

Page of GA34-0003-6, -7As Updated August 20, 1976By TNL GN34-0340DCB Word 6 (Word count)This word contains a count of the number of words to be transmitted or received.DCB Word 7 (Starting data address)This word contains the starting address in System/7 storage to be used in fetching or storingdata for a transmit or receive operation. After the DCB has been placed in the variousBSCA registers, this address is placed in the BSCA SAR which determines the storageaddress of the data being handled by the BSCA. On transmit operations, one word is takenfrom storage by a cycle steal operation and is transmitted as two consecutive characters. Onreceive operations, two characters are received and stored in a buffer. Then a cycle stealoperation is initiated to transfer them to storage as one word. If an odd number of charactersis received, zeros are loaded into the low order byte.Write Address0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA0 0 0 0 1 XXX 0 0 1 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 0 0 0 0 01 I I I II II I I I I III 1 1 1 111110 8-F 2 0 3 3 0 0This command stores the contents of bits 8-15 from the register specified by the Rfield, or the accumulator if R=000, into the BSCA storage address register (SAR) bits8-15, to form a partial DCB address. Condition code 2 is set if the BSCA is busy oran interruption is pending. This command does not cause an interruption.Initiate I/O0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA0 0 0 0 1 X X X 0 0 1 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0I I I I 1 1 1 1 I I I I 1 1 1 1 1 1 1 1 1 1 1 1 10 8-F 2 0 7 3 0 0This command stores the contents of bits 8 to 15 from the register specified by the Rfield, or the accumulator if R= 000, into the the BSCA storage address register (SAR),bits 0 to 7, to complete the DCB address. Condition code 2 is set if the BSCA is busy oran interruption is pending. If the BSCA has not been prepared, condition code 1 is returnedand command reject (bit 1) is set in the direct control channel status word. If theBSCA has been prepared, the DCB is fetched from storage by the adapter. Subsequentaction depends on the control bit(s) in word 3 of the DCB as described earlier in thischapter.8-8 GA34-0003