Publication 1747-UM006B-EN-P - June 2003
3-14 Addressing
How Specialty I/O Module Images Are Mapped
Specialty I/O module images are discretely mapped or block transfer
mapped, depending on the specialty I/O mode you have selected for
the 1747-ASB module. SW3-7 provides two specialty I/O modes,
discrete and block transfer.
When Block Transfer Mode is Selected
The advantage of using block transfer mode is that it only requires
one byte of the 1747-ASB module's input and output image.
However, you must add block transfer instructions to your PLC user
program, and block transfer times are generally longer than discrete
transfer times.
When block transfer mode is selected, all specialty modules that are
block transfer mapped use one byte in the 1747-ASB module's input
and output image. These bytes reside in the least significant byte of
the 1747-ASB image reserved for the module's slot.
When a module is block transfer mapped, the module's input and
output image is transferred on the RIO link using RIO block transfers.
RIO block transfers are processed by the scanner and 1747-ASB
module. The 1747-ASB module transfers the specialty I/O modules
image by way of a backplane scan. The 1747-ASB module then
transfers the image to the scanner using RIO block transfers.
151413121110987 654 3210
group 0
group 1
group 2
group 3
group 4
group 5
001 1
1747-ASB Module Input Image
65432
1
slot 1
slot 2
slot 3
slot 4
slot 5
slot 6
PLC Local Chassis
Processor/Scanner
SLC Local Chassis
Scanner
Processor
Backplane transfer from a 4-point discrete
input module to the 1747-ASB module image.
4-Point Input Module Data
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