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

The function of each control character follows.MnemonicFunctionSOH or STX Reset control mode and set the adapter to text mode.ETB or ETX Reset text mode with block check character (BCC) comparison.EOT End of transmission.ENQ Reset text mode without BCC transmission and comparison.NAK Negative response to a request for a reply, or to a block ofheading, or a block of text in error.SYN Transmitted automatically by the adapter to establish and maintainsynchronization.DLE Alert the adapter to test the next character for a defined controlsequence. In nontransparent text mode, DLE is treated as data.In transparent text mode, the transmitter adds a second DLE aftereach data DLE. At the receiver, the first DLE is stripped off anddoes not enter storage or the BCC.ITB Included in the BCC; it causes the BCC to be sent or received.IPL Control characters to decode an IPL sequence.ACK 0 Indicate affirmative acknowledgement to even blocks.ACK 1 Indicate affirmative acknowledgement to odd blocks.WACK Indicate a temporary not ready to continue/receive condition.DISC Used on switched communication facilities only, to initiate adisconnect.RVI Reverse direction of data transfer.TTD Alert the receiving station to a temporary time delay.XSTX Turn off control mode and set the adapter to transparent text mode.XITB Same as ITB, but also turn off transparent text mode.XETX or XETB Same as ETB or ETX but also turn off transparent mode.XSYN Transmitted automatically by the adapter to establish and maintainsynchronization in transparent text mode.XENQ Turn off transparent text mode.XTTD Alter the receiving station to a temporary time delay in transparenttext mode.XDLE Alert the adapter to test the next character for a defined controlsequence in transparent text mode. The transmitter adds a secondDLE after each data DLE. At the receiver, the first DLE isstripped off and does not enter storage or the BCC.Synchronization and Timing InformationThe BSCA receives strobing pulses from the modem which establish and maintain bitsynchronization. If the modem does not supply a strobe, the Internal Clock Feature mustbe installed to supply synchronization. Whichever form of bit synchronization is used, aspecific series of characters precedes each transmission in order to establish charactersynchronization.Leading Pad CharactersIf the Internal Clock feature is being used, BSCA automatically begins transmission withtwo leading pad characters (Hex 55) followed by the initial synchronizing pattern of twoSYN characters.Binary Synchronous Communications Adapter 8-4.1Fmcww■(qc rimr.P.R• Pew,