Publication 1747-RM001G-EN-P - November 2008
8-6 Block Transfer Instructions
In addition to the control and status bits, the control block contains two other
parameters the processor uses to execute the block transfer instructions.
Requested Word Count, Word 1 (RLEN)
This is used to configure BTR/BTW length information (0 to 64). Length is
the number of BTR/BTW words read from or written to the RIO device. If
RLEN = 0 for a BTW instruction, 64 words are sent. If RLEN = 0 for a BTR
instruction, the actual length is determined by the RIO device responding to
the block transfer read request.
Transmitted Word Count/Error Code, Word 2 (DLEN)
Transmitted Word Count is the status of the actual number of BTW words
sent or the number of BTR words received. The processor uses this number to
verify the transfer. This number should match the requested word count
(unless the transmitted word count is zero). If these numbers do not match,
the processor sets the ER bit (bit 12). If there is an error, the processor gives
the error code in Word 2 of the control structure in the form of a negative
number. See Table 8.4, “BTR/BTW Error Codes,” for a list of error codes.
Only one error code is stored at a time (a new error code overwrites the
previous error code).
Table 8.4 BTR/BTW Error Codes
Error Code Description
0 The block transfer completed successfully.
-6 Illegal block transfer length requested.
-7 Block transfer communication error occurred when block transfer
request was initiated.
-8 Error in block transfer protocol.
-9 Block Transfer Time-out - Either the SLC user program cancelled the
block transfer or the scanner’s block transfer timer timed out. Note
that a time-out error occurs if a block transfer is attempted at a
location that is not configured for block transfer operation (for
example, requesting a block transfer for a location that is an output
module).
-10 No RIO channel configured.
-11 Attempted a block transfer either to a non-configured block transfer
device (i.e., an invalid logical rack, group, or slot), or at a
complementary device location where there is no corresponding
primary image space allocated.
-12 Attempted a block transfer to an inhibited device.
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