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

I/0 COMMANDSThe ACCA is programmed using the prepare I/O command as described in Chapter 4 under"Input/Output Instruction." Data is transferred between the processor and the ACCA byimmediate read and immediate write commands. The setting of the modifier field bits inan immediate command further defines the operation to be performed.All I/O commands to the ACCA must have a device address of 001100 and a moduleaddress of 000000.The terms "status" and "mode" as used in the I/O command descriptions have differentmeanings. While in either transmit or receive mode, the ACCA accumulates a logitudinalredundancy check (LRC) character. Figure 7-4 shows a line control sequence forboth point-to-point and dial-up operation. These methods are the same but in dial-upoperation a communication line is connected and disconnected through a data set.The ACCA enters transmit status upon receiving a transmit control command in orderto establish a data link and to block any possible incoming data. The ACCA enters transmitmode when it detects an EOA character in a transmit character command. This EOAcharacter is not accumulated in the LRC register, but any following EOA characters areconsidered as data and accumulated in the LRC register.The ACCA enters receive status when it detects a start bit from a remote processor.The ACCA returns to standby mode after the received character is deserialized unlessthat character is an EOA. If the character is an EOA, the ACCA enters receive mode. ThisEOA character is not accumulated in the LRC register, but any following EOA charactersreceived are considered as data and accumulated in the LRC register.The ACCA is in standby mode when it can accept transmit commands or receive data.When in standby mode, the ACCA decodes all characters received except upshift anddownshift (including line noise) and presents the decoded characters to the program asdata.The ACCA exits from transmit or receive mode and then enters standby mode underany one of these conditions:• The ACCA detects an end-of-transmission (EOT) character• A time-out interruption request occurs• A reset ACCA command is issued by the System/7 programPoint-to-pointEOA EOB EOB EOB EOT NAK YAK YAKSystem/7 or host LRC LRC le/LRCNon-switched lineText ....Text A Text A A A A A A AWWWW.—,W Text Text w Text wSystem/7 or host LRC v LRC LRCNAK YAK YAK EOA EOB EOB EOB EOTDial-upSystem/7 or host ConnectSwitched networkAAANAKYAK EOA EOB E.OT DialLRC Disconnect— ....- .......-....,A A Text AW Text W W r •• w W.--,Text.-.■-■System/7 or host I Dial A U LRC LRC DisconnectEOA EOB EOB EOTYAKFigure 7-4. Point-to-point and dial-up operationAAsynchronous Communications Control Attachment 7-7!ANIWWWIAii,111W.1.11111••••