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

1111 Minn. 11111111R !VW IMF" !PFLINE CONTROLA precise exchange of control characters between computers is necessary to establish andmaintain teleprocessing communications. This exchange of control characters is calledline control. One of its functions is to prevent two or more stations, terminals, orSystem/7s from attempting to use the line simultaneously (line contention).Line Control CharactersAs the following table shows, the line-control characters (signals) are represented in shorthandform as acronyms. Some of the acronyms also have equivalent encircled letters. Theseare referred to as "circle C, circle D," etc. This form is used in programming, as well as incommunications and line-control discussions.Character Function Acronym Binary Hexadecimal (PTTC)End of transmission EOT ® 0001 1111 1FEnd of address EOA ® 0001 0110 16End of block EOB 10 00 11 1101 3DPositive response YAK 0 0111 0110 76Negative response NAK CD 0100 0000 40Start of address SOA ® 0011 0111 37Upshift US 0001 1100 1CDelete DEL 0111 1111 7FDownshift DS 0111 1100 7CSpace SP 0000 0001 01All characters except US and DS are presented as data when the ACCA is in standbymode. EOB, the first EOT at the end of transmission, US, YAK, NAK, SOA, and SP(SP when used in addressing and polling sequences) are not presented as data.The function of line control character signals is as follows:Acronym FunctionEOTEOA 0EOB 0YAK 0Indicates end of transmission; resets ACCA to standby mode and,if station control option is installed, resets ACCA to unselectedstatus.Switches ACCA from receive mode to transmit mode and viceversa. This signal starts the LRC counter at both the sending andreceiving terminals. The EOA signal is not included in the LRCcheck that follows it.Indicates the end of a unit-block of text. This is followed by theLRC character, which provides an LRC check comparison at thereceiving system with the EOB character included in the check.Indicates a positive response (Yes). It is coded as a period characterand indicates a positive response to an address or a positiveanswer to an EOB/LRC sequence.74 GA34-0003