8-8Communicating with Extended-Local I/O

Example Calculations:

Here is an example system that provides sample calculations of a worst case block-transfer completion time and the completion time of the modules in chassis 2.

PLC-5/40L Processor

Channel 2

Processor-

Resident

I/O

No BT modules

Extended-Local I/O Chassis 1

1771-ALX

 

Adapter

2 BT

Module

modules

 

 

 

 

 

 

 

 

Extended-Local I/O Chassis 2

1771-ALX

 

Adapter

1 BT

Module

 

 

modules

 

 

 

 

 

 

Extended-Local I/O Chassis 3

1771-ALX

 

Adapter

No BT

Module

modules

 

 

 

 

 

 

 

 

Extended-Local I/O Link

The logic scan completes in 15 ms. Housekeeping completes in approximately 6 ms (as calculated in the formula on page

NO TAG). The longest block-transfer request is 20 words.

 

Worst-case time (T) = D X R

 

 

 

D = 2E

L + (0.1W) and R = 1

Because 10 < 15 (which is the logic scan)

 

D (ms) = (2

2)

(2) + (0.1

20 )]

 

 

D = 10 ms

 

 

 

 

 

T = 10

1

 

 

 

 

 

T = 10 ms

 

 

 

 

 

 

 

 

 

 

Completion time (T) for module in chassis 2 transfer: = D X R

 

Block-transfer length = 20

 

 

 

 

D = 2E

 

M + (0.1W)

and R = 1 Because 6 < 15 (which is the logic scan)

 

D (ms) = (2

2)

(1) + (0.1

20 )]

 

 

D = 6

ms

 

 

 

 

 

 

T = 6

 

1

 

 

 

 

 

T = 6

ms

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Considerations for Extended-local Racks

The following are programming considerations when you are transferring block data in an extended-local rack:

Block-transfer instructions to any of the following modules that reside in an extended-local rack will result in frequent checksum errors:

1771-OFE1, -OFE2, and -OFE3 modules, all versions prior to series B, revision B

IMC-120 and IMC-123, all versions

Publication 1785-UM012D-EN-P - July 2005

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Bradley Smoker PLC-5 user manual Considerations for Extended-local Racks, 8Communicating with Extended-Local I/O