1. xerox 560 computer system - The UK Mirror Service

Transfer in Channel. A control lOCO containing a Transferin Channe I command has the fo Ilowi ng format:LocationsOescri pti on of CommandA +6, A + 7 Transfer in Channel to location A +4.A+8,A+9StopThe Transfer in Channel command is executed within thelOP and has no direct effect on any of the I/o elementsexternal to the addressed lOP. The primary purpose of thiscommand is to permit branching within the command list(i. e., fetching the next operational lOCO from a pair ofmemory word locations other than the next two consecutiveword I ocati ons).When the lOP executes the Transfer in Channel command,it loads the command address register of the appropriateI/o subchannel with the contents of bit positions 13-31(the "next command doubleword address" field), fetchesand loads the new operational 10CD into appropriate registerswithin the I/O subchannel and order register withinthe device controller/device (unless data chaining is specified),and then executes the new lOCO. (Bit positions8-12 and 32-61 are ignored and should be coded aszeros. )If data chaining or command chaining is specified in thelOCO preceding the lOCO containing a Transfer in Channelcommand, the chaining flags are not significant to noraltered by the Transfer in Channel command.When used in conjunction with command chaining, Transferin Channel command faci litates the control of devi ces suchas unbuffered card punches or unbuffered line printers. Forexample, assume that it is desired to present the same cardimage twelve times to an unbuffered card punch. The punchcounts the number of times that a record is presented to itand automatically generates a "chain modifier" signal whentwelve rows have been pu·nched. The command addressregister within the I/o subchannel is incremented by twoby the "chain modifier" signal and the next consecutivelOCO within the command list is skipped over (not fetchedor executed). A command list for punching two cards mightbe as shown in the following example:The Transfer in Channel command can be used also in conjunctionwith data chaining. As one example, considera situation often encountered in data acquisition applications,where data is transmitted in extremely long, contiguousstreams. In this case, the data can be storedalternately in two or more buffer storage areas so thatcomputer processing can be carried out on the data in onebuffer whi Ie additional data is being input into the otherbuffer. The command list for such an application might beshown in the following example:LocationsOescri pti on of CommandB, B + 1 Read data, store in buffer 1, data chain.B+2, B+3Store into buffer 2, data chain.B+4, B+5 Transfer in Channel to location B.If the lOP encounters two successive Transfer in Channelcommands, an lOP control error (IOPCE) occurs and theI/O operation is terminated immediately. An 10PCE isreported as status information (bit 13 of register Rul) whenthe BP executes an SIO, HIO, no, or TOV instruction.STOPA control lOCO with a Stop command has the followingformat:LocationsDescription of CommandA, A + 1 Punch row for card 1, command chain.A + 2, A + 3 Transfer in Channe I to locati on A.A +4, A +5Punch row for card 2, command chain.The Stop command causes certain devices to stop, generatea "channel end II signal, and also request an I/o interruptif bit 0 in the lOCO is coded as a 1. If the I/O interruptInput/Output Processor (lOP) Fundamentals 147