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

specified by the channel command word (CCW). Thenumber of bytes is determined by the CCW bytecount. Status returned by the adapter during initialselection will be 0, and ending status will bechannel end and device end. If the adapter has previouslyaccepted an XIO initialize read or XIO initializewrite from the 1800 and the System/360 has notyet issued the complementary command, attention isalso given with ending status.The contents of the two bytes of sense datastored depend on the conditions in the adapter, asshown in Figure 114.The only exception to the sense operationdescribed in the preceding paragraphs occurs whenthe System/360 issues a sense command before aprevious control command has been cleared anddevice end accepted for the control command. Ifthe control has not been cleared by an XIO sensedevice from the 1800, the adapter responds withbusy, which results in a condition code of 2, busy.If the control has been cleared, but device end hasnot yet been accepted or has been stacked by theSystem/360, the adapter responds with busy anddevice end. This response results in a conditioncode of 1, status stored and clears device end fromthe adapter, leaving the adapter idle.Read or Read Backward (System/360)The primary function of a read or read backwardcommand is transmission of data from the 1800 tothe System/360. The adapter recognizes no differencein the function to be performed by these twocommands. However, the suppress interrupt bit(S) is not available in the read backward command.Therefore, the interrupt to the 1800 cannot be suppressedwhen using the read backward command.Either a read or a read backward command may beused as the complementary command to an XIOinitialize write from the 1800. The adapter responseConditionHigh-Order BufferLow-Order BufferBYTE 1 BYTE 2Adapter Idle Undefined Undefined1800 Previously Issued:XIO Initialize Read Area/Function ModifierXIO Initialize Write Area/Function ModifierXIO Control Zero ZeroFigure 114. Sense Bytes Presented to System/36017446B jto a System/360 read or read backward commanddepends on the status of the adapter, according tothe following rules.IDLE ADAPTER: An idle adapter accepts a readcommand 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 initializewrite) from the 1800. Unless suppressed by the S-bitbeing on in the command byte, a 360 command storedinterrupt is generated by the adapter to signal the1800 of the pending operation. The complete commandbyte (including modifiers) is saved by theadapter and is available to an XIO sense device fromthe 1800.WAITING XIO INITIALIZE WRITE: An adapter holdinga previously accepted XIO initialize write fromthe 1800 accepts a System/360 read 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 write. ) Both the XIO initialize write andSystem/360 read operations are initiated. The datatransfer operation continues until the System/360byte count for the read or the 1800 word count forthe XIO initialize write is decreased to 0, or untilan error condition is detected. If neither channel isdata chaining when the byte count or word countreaches 0, channel end and device end is given to theSystem/360. Acceptance of the ending status by theSystem/360 releases the adapter and returns it toidle. The 1800 system is signaled by a transfer endinterrupt. If the System/360 terminated the operation,the halt indicator will also be on in the devicestatus word (DSW).BUSY ADAPTER: A System/360 read command maybe rejected because of any one of the followingadapter busy conditions:1. A System/360 read 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 read command is issued after aprevious control command has been cleared, butbefore device end has been accepted by the System/360.In this case, the adapter respondswith busy and device end. This response results216