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

NAK 0 Indicates a negative response (No). It is coded as a hyphen characterand indicates a negative response to an address, a poll, or anEOB/LRC sequence.SOA QS Indicates a start-of-address condition. It is coded as a commacharacter and is used when the station control feature is installed.US Indicates that the characters that follow will be uppercase until aDS, EOB, or EOT character is decoded.DEL One of the line control characters used in a sequence to causeSystem/7 to enter IPL mode from standby mode. This sequenceis as follows:1. EOA2. US3. DEL4. DSDS Indicates that the characters that follow will be lowercase until aUS is decoded. Two consecutive DS characters put the ACCA intobinary mode.SP This signal is coded as a character with no bits. It is used in stationcontrol addressing and polling.The ACCA uses the line control characters in a manner similar to the way in which theIBM 2740 Communication Terminal Model 1 uses them. For more detail on line controlof the 2740 Communication Terminal, refer to the manual IBM 2740 CommunicationTerminal Models 1 and 2 Component Description, Order No. GA24-3403.STATION CONTROLA station control option installed in the ACCA connects the System/7 to a communicationsline that is shared with other teleprocessing devices or systems. The System/7 isselected by a host processor when the host transmits the sequence of characters EOT,SOA, ADDRESS (unique for each device on the communications line), and SPACE (seeFigure 7-2).HostNon-switched lineEOT SOAEOA EOB EOB EOT00 Address SP 0 ®LRC OLRC 0A Text A Text ASystem/70 0YAK YAK YAKor or0 0NAK NAKFigure 7-2. Station control (addressing) operationAsynchronous Communications Control Attachment 7-5