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

Bit 1-Reserved.Bit 2-Transmit Operation. A 3-second timeout starts, and request to send to the modemis turned on. When clear to send from the modem comes on, the timeout is turned offand the BSCA begins transferring data from System/7 storage. A normal channel-end/device-end interruption request to the System/7 processor is generated when:• A COD character is transmitted and the chaining flag (described later in this section)is off.• When the word count becomes 0 and the chaining flag is off.If the data set ready line from the modem is off, or if receive mode is on while attemptingto transmit, an error interruption occurs immediately, setting on bit 1 (commandreject) in the ISW. Receive mode will be on if the previous operation was a receive operationand a COD character was not received.Failure to receive clear to send from the modem within the 3-second timeout periodcauses an interruption, setting on bit 3 (timeout) in the ISW. Transmit mode is turned offand request to send to the modem is discontinued after the PAD character (eight 1-bits) issent following a COD character or block check character (BCC) if required.Bit 3-Allow Transparent Control. The ability to transmit control sequences while in transparenttext mode is provided by setting on this bit. It should be set on in the final DCBused for a transparent text operation. It can be used only in a DCB following a block oftransparent text.If the BSCA is not in transparent text mode when this bit is presented, an error interruptionoccurs setting on bit 1 (command reject) in the ISW.Programming note. It is suggested that bit 3 be used only with a word count of 1 (transparentend of text-DLE ETX; transparent end of transmission block-DLE ETB, etc.) toavoid unpredictable results should a data character and a DLE character have the samebit configuration.Bit 4-Enable Terminal. If the host attach switch on the System/7 console is in the enableposition, setting on this bit sets the data terminal ready and enables detection of dataset ready. In a switched network, if the host attach switch is in the enable and IPLposition, a. ring indication also sets the data terminal ready. In a non-switched network, thedata terminal is ready at all times.Bit 11 (start 3-second timer) may be used with bit 4 to limit the time allowed by theBSCA for the data set to get ready. If the data set is not ready within this time, an interruptionoccurs, setting on bit 3 (timeout) in the ISW.Bit 5-Disable Terminal. Setting on this bit discontinues the data terminal ready line to thedata set, to allow disconnecting from a switched network. During this period (3 seconds)the BSCA is busy. At the completion of the disconnect, the BSCA causes an interruption ifthe chaining flag in word 5 of the DCB is off. Data terminal ready cannot be discontinuedon a leased line.Note: If the System/7 is dialed up erroneously, or if a switched line connection is interruptedduring BSCA communications, then the data terminal ready line to the data setmust be discontinued before line connection can be re-established. There are 3 ways ofdoing this:1. Set on bit 5 to disable the terminal.2. Put the host attach switch on the operator console in the disable positionmomentarily.3. An automatic internal timer disables the terminal after 2.5 minutes.8-6 GA34-0003