Xerox 560 Reference Manual page 153

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Transfer in Channel. A control lOCO containing a Transfer
in Channe I command has the fo Ilowi ng format:
The Transfer in Channel command is executed within the
lOP and has no direct effect on any of the I/o elements
external to the addressed lOP. The primary purpose of this
command is to permit branching within the command list
(i. e., fetching the next operational lOCO from a pair of
memory word locations other than the next two consecutive
word I ocati ons).
When the lOP executes the Transfer in Channel command,
it loads the command address register of the appropriate
I/o subchannel with the contents of bit positions 13-31
(the "next command doubleword address" field), fetches
and loads the new operational 10CD into appropriate reg-
isters within the I/O subchannel and order register within
the device controller/device (unless data chaining is spec-
ified), and then executes the new lOCO.
(Bit posi-
tions 8-12 and 32-61 are ignored and should be coded as
zeros. )
If data chaining or command chaining is specified in the
lOCO preceding the lOCO containing a Transfer in Channel
command, the chaining flags are not significant to nor
altered by the Transfer in Channel command.
When used in conjunction with command chaining, Transfer
in Channel command faci litates the control of devi ces such
as unbuffered card punches or unbuffered line printers. For
example, assume that it is desired to present the same card
image twelve times to an unbuffered card punch. The punch
counts the number of times that a record is presented to it
and automatically generates a "chain modifier" signal when
twelve rows have been pu·nched. The command address
register within the I/o subchannel is incremented by two
by the "chain modifier" signal and the next consecutive
lOCO within the command list is skipped over (not fetched
or executed). A command list for punching two cards might
be as shown in the following example:
Locations
Description of Command
A, A + 1
Punch row for card 1, command chain.
A + 2, A + 3
Transfer in Channe I to locati on A.
A +4, A +5
Punch row for card 2, command chain.
Locations
Oescri pti on of Command
A +6, A + 7
Transfer in Channel to location A +4.
A+8,A+9
Stop
The Transfer in Channel command can be used also in con-
junction with data chaining. As one example, consider
a situation often encountered in data acquisition applica-
tions, where data is transmitted in extremely long, con-
tiguous streams.
In this case, the data can be stored
alternately in two or more buffer storage areas so that
computer processing can be carried out on the data in one
buffer whi Ie additional data is being input into the other
buffer. The command list for such an application might be
shown in the following example:
Locations
Oescri pti on of Command
B, B
+
1
Read data, store in buffer 1, data chain.
B+2, B+3
Store into buffer 2, data chain.
B+4, B+5
Transfer in Channel to location B.
If the lOP encounters two successive Transfer in Channel
commands, an lOP control error (IOPCE) occurs and the
I/O operation is terminated immediately.
An 10PCE is
reported as status information (bit 13 of register Rul) when
the BP executes an SIO, HIO, no, or TOV instruction.
STOP
A control lOCO with a Stop command has the following
format:
The Stop command causes certain devices to stop, generate
a "channel end
II
signal, and also request an I/o interrupt
if bit 0 in the lOCO is coded as a
1.
If the I/O interrupt
Input/Output Processor (lOP) Fundamentals
147

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