Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 51)

Publication 1747-UM006B-EN-P - June 2003
Addressing 3-15
The scanner and 1747-ASB module process a maximum of one RIO
block transfer per logical device per RIO scan. If you wish to perform
four RIO block transfers for a logical device, at least four RIO scans
are required to complete these RIO block transfers.
The 1747-ASB module can block transfer up to a maximum of 8 words
per block transfer.
The 1747-ASB module processes RIO block transfers that are less than
or equal to the specialty I/O module's image size. For example, if a
four word specialty I/O module is block transfer mapped, the
1747-ASB module accepts RIO block transfer reads for this module if
they are less than or equal to four words. RIO block transfers always
begin reading or writing word 0 (least significant word) of the
module's image.
An RIO block transfer size of zero will cause all of the module's image
to be transferred.
When Discrete Mode is Selected
The advantage of discrete mode is that no programming is required
for data transfer. However, discrete mode requires more 1747-ASB
module image space than block transfer mode.
1747-ASB Module Input Image
1747-ASB Module Output Image
Block Transfer Byte
1 5 1 4 1 3 1 2 11 1 0 9 8 7 6 5 4 3 2 1 0
Block Transfer Byte
1 5 1 4 1 3 1 2 11 1 0 9 8 7 6 5 4 3 2 1 0
The byte reserved in the
1747-ASB module’s output and
input image is used by the
scanner and 1747-ASB module to
process the RIO block transfer
.
1747-ASB module exchanges data with
the speciality I/O module via the
backplane.
The PLC scanner and
1747-ASB module
exchange
the specialty I/O module’s
data using RIO block
transfers.
1747-ASB module is
configured for 1-slot
addressing.
6 5 4 3 2 1
slot 1
slot 2
slot 3
slot 4
slot 5
slot 6
slot 1
slot 2
slot 3
slot 4
slot 5
slot 6
PLC Local Chassis
Processor/Scanner