Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 87)

Publication 1785-UM012D-EN-P - July 2005
Communicating with Remote I/O 6-15
Block-Transfer Minor Fault Bits
Block-Transfers of
Remote I/O Data Block-transfers of I/O data to remote I/O follow these guidelines:
• Block-transfer data exchange and the program scan run independently
and concurrently. Once block-transfers are initiated, the controller
performs them asynchronously to the program scan.
• During every remote I/O scan, the Controller performs a maximum of
one block-transfer per entry in the scan list.
Minor Fault Description
S:17/0Block-transfer queue full to remote I/O There is a possibility that the PLC-5 controller might temporarily be unable to
initiate multiple consecutive user-programmed block-transfers. For any
block-transfer which temporarily can’t be processes, the PLC-5 controller sets minor
fault bit S:17/0 and skips that block-transfer instruction. This condition is
self-correcting, but bit S:17/0 remains set until you reset it. You can avoid this
minor fault be separating block-transfer instruction rungs with other rungs.
S:17/1 through S:17/4Queue full - channel xx The PLC-5 controller can process a maximum of 64 remote block-transfers per
channel pair (1A/1B or 2A/2B). This maximum includes:
block-transfers that are currently in the active buffer
initialized block-transfers that are waiting for execution in the holding queue
Once the 64 block-transfer maximum is reached, the following minor fault bits are
set, depending on which channel pair is involved:
Channel pair:Minor fault bits set:
1A/1BS:17/1 and S:17/2
2A/2BS17:3 and S:17/4
The PLC-5 controller won’t initialize any remote block-transfer instruction which
exceeds the 64 maximum. The .EW, .DN, and .ER bits are reset on any
block-transfer which exceeds the 64 maximum. This condition is self-correcting, but
the bits remain set until you reset them.
S:10/7No more command blocks exist This minor fault bit is normally associated with an application programming
problem, but this bit can also be set when using block-transfers if the maximum
number of command blocks available in the PLC-5 controller is exceeded. The
command blocks are used by both the local and remote block-transfers.
PLC-5 type:Maximum number of command blocks:
PLC-5/11, -5/20, -5/30128
PLC-5/40256
PLC-5/60, -5/80384
This condition generally occurs when a program attempts to repeatedly initialize
block-transfers which have not yet completed with a .DN or .ER bit. This condition
is self-correcting, but bit S:10/7 remains set until you reset it.