Systems Reference Library - All about the IBM 1130 Computing ...

in a condition code of 1, status stored andclears device end from the adapter leaving theadapter idle.3. A System/360 read command is issued after theadapter has previously accepted an XIO initializeread from the 1800. In this case, the adapterresponds with busy and attention. This responseresults in a condition code of 1, status stored.If the attention status generated by the XIO initializeread was not previously accepted, thisresponse clears that status. As a result, attentionstatus no longer attempts to interrupt theSystem/360. However, attention still appearsas a response to any read command until thepreviously accepted XIO initialize read has beensatisfied.Write (System/360)The primary function of a write command is transmissionof data from the System/360 to the 1800.Write is the complementary command to an XIOinitialize read from the 1800. The adapter responseto a System/360 write command depends on thestatus of the adapter, according to the followingrules.IDLE ADAPTER: An idle adapter accepts a writecommand by responding during initial selection with0 status. This response results in a conditioncode of 0, operation initiated. System/360 channeloperation is then suspended until the adapter receivesthe complementary command (an XIO initializeread) from the 1800. Unless suppressed by theS-bit being on in the command byte, a 360 commandstored interrupt is generated by the adapter to signalthe 1800 of the pending operation. The completecommand byte (including modifiers) is saved by theadapter and is available to an XIO sense device fromthe 1800.WAITING XIO INITIALIZE READ: An adapter holdinga previously accepted XIO initialize write fromthe 1800 accepts a System/360 write command byresponding to initial selection with 0 status. Thisresponse results in a condition code of 0, operationinitiated. (The adapter responds with 0 statusregardless of whether or not the System/360 hasaccepted the attention status generated by the XIOinitialize read. ) Both the XIO initialize read andSystem/360 write operations are initiated. Thedata transfer operation continues until the System/360 byte count for the write or the 1800 word countfor the XIO initialize read is decreased to 0, oruntil an error condition is detected. If neither channelis data chaining when the byte count or wordcount reaches 0, channel end and device end aregiven to the System/360. Acceptance of the endingstatus by the System/360 releases the adapter andleaves it idle. The 1800 system is signaled by atransfer end interrupt. If the System/360 terminatedthe operation, the halt indicator will also be on inthe device status word.BUSY ADAPTER: A System/360 write commandmay be rejected because of any one of the followingadapter busy conditions:1. A System/360 write command is issued before aprevious control command is cleared by an XIOsense device from the 1800. In this case, theadapter responds with busy. This responseresults in a condition code of 2, busy.2. A System/360 write command is issued after aprevious control command has been cleared, butbefore device end has been accepted by theSystem/360. In this case, the adapter respondswith busy and device end. This response resultsin a condition code of 1, status stored and clearsdevice end from the adapter, leaving theadapter idle.3. A System/360 write command is issued after theadapter has previously accepted an XIO initializewrite from the 1800. In this case, the adapterresponds with busy and attention. This responseresults in a condition code of 1, status stored.If the attention status generated by the XIOinitialize write was not previously accepted,this response clears that status. As a resultattention no longer attempts to interrupt theSystem/360. However, attention still appearsas a response to any write command until thepreviously accepted XIO initialize write has beensatisfied.Test I/O (System/360)A test I/0 may be used to obtain the status of theadapter any time the System/360 channel is available.The status received indicates the condition ofthe adapter as follows:ZERO STATUS: This status indicates that theadapter was idle at the time of response and resultsin condition code of 0, available.BUSY: This status indicates that a control commandpreviously issued by the System/360 was not acceptedby the adapter and results in a condition code of 2,busy.System/360 Adapter 217