Publication 1747-UM013B-EN-P - January 2005
RIO Block Transfer
5-5
Using Block Transfer
Instructions (BTR and BTW)
Block transfer instructions are supported by SLC 5/03 (OS302,
Series C), SLC 5/04 (OS401, Series C) and SLC 5/05 (OS501, Series C)
and higher processors only. For application examples for block
transferring with SLC 5/02 processors, refer to Appendix D. With
block-transfer instructions, you can transfer up to 64 words to or from
a remote device over an Allen-Bradley Remote I/O (RIO) link. A
Block Transfer Read (BTR) is used to receive data from a remote
device. A Block Transfer Write (BTW) is used to send data to a remote
device. The RIO Series B scanner (1747-SN) and the back-up scanner
(1747-BSN) perform block transfers via M0 and M1 file buffers.
A false-to-true rung transition initiates a BTW or BTR instruction. The
BTW instruction tells the processor to write data stored in the BTW
Data File to a device at the specified RIO rack/group/slot address. The
BTR instruction tells the processor to read data from a device at the
specified RIO rack/group/slot address and store it in the BT Data File.
A total of 32 block transfer buffers are available; you can execute a
maximum of 32 different block transfers. The processor runs each
block transfer request in the order it is requested. When the processor
changes to Program mode, all pending block transfers are cancelled.
A BTR or BTW instruction writes information into its control structure
address (a three-word integer Control Block) when the instruction is
entered. The processor uses these values to execute the transfer.
You must enter an M1 file address into BTR Instructions and an M0 file
address into BTW Instructions. However, each instruction uses both
the M0 and M1 file for that buffer number (1 through 32). For
example, to use the first available buffer (1) for a BTR, enter M1:e.100
into the “Buffer File” field. However, M0:e.100 is also used by this
BTR. So, the next BT instruction must use another M-file buffer
(2 through 32).
RIO Block Transfer General Functional Overview
The RIO scanner performs block transfers through control/status
buffers allocated in the scanner’s M0 and M1 files. For BTW’s, the data
stored in the File is copied into the M0 block transfer buffer, the M0
block transfer buffer is then transferred to the RIO device. The
corresponding M1 block transfer buffer contains only BTW status
information. For BTR’s, the M0 block transfer buffer contains only BTR
control information. The actual data read from the remote device is
received in the scanner’s M1 block transfer buffer. This data is then
copied into the BTR Data File. A total of 32 block transfer
control/status buffers exist in the M0 (output/control) and the M1
(input/status) files.
EN
DN
ER
BTR
Block Transfer Read
Rack
0
Group
0
Slot
0
Control Block
N10:140
Data File
N21:100
Buffer File
M1:1.3200
Requested Word Count
0
Transmitted Word Count
0
EN
DN
ER
BTW
Block Transfer Write
Rack
0
Group
0
Slot
0
Control Block
N10:10
Data File
N20:0
Buffer File
M0:1.100
Requested Word Count
0
Transmitted Word Count
0
BTW
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