Bradley Smoker PLC-5 user manual Description

6-14Communicating with Remote I/O

Maximum Number of

Active Buffers

Per Remote I/O Channel

PLC-5/60, -5/60L, -5/80, -5/80E 23

PLC-5/40, -5/40L, -5/40E	31
PLC-5/30	39
PLC-5/20, -5/20E	43
PLC-5/11	43

Placing the controller in program mode, cancels block-transfers in the active buffers and in the waiting queues.

As shown in the previous figure, the controller has the following storage areas for block-transfers:

Storage Area	Description
active buffers	store initialized block-transfer requests for a channel
	The adjacent table lists the maximum active buffers for each
	enhanced and Ethernet PLC-5 controller.
	The controller places a block-transfer request directly into the
	active buffer only if: a buffer is available and no block-transfers to
	the slot is in the queue.
waiting queues	store block-transfer requests that cannot be placed into the active
	buffer because:
	all of the channel’s active buffers are being used
	the slot addressed by the block-transfer is currently processing a
	block-transfer

Once a block-transfer to a slot completes, the controller checks the queue to see if a block-transfer addressed to the slot is waiting. If one exists, the controller moves it to the active buffer.

Since a controller can request a block-transfer from every slot in a chassis concurrently, the adapter device chooses the order in which the block-transfers execute on the chassis. Block-transfer requests are processed differently in fault routines, selectable timed interrupt routines (STI), and controller input interrupt routines (PII); see chapters 16, 18, and 19 respectively for more information.

Publication 1785-UM012D-EN-P - July 2005