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Peripheral Servicing Priority Mode Section 6-9
with common codes beginning with 01 Hex or forced set/reset commands with
common codes beginning with 23 Hex) and 2) Servicing any received C-mode
commands that access I/O memory (excluding NT Links using the peripheral
or RS-232C port).
6-8-2 Parallel Processing Mode and Minimum Cycle Times
If a minimum cycle time is specified when a parallel processing mode is being
used, a wait will be inserted after program execution until the minimum cycle
time has been reached, but peripheral servicing will continue.
6-8-3 Data Concurrency in Parallel Processing with Asynchronous
Memory Access
Data may not be concurrent in the following cases when using Parallel Pro-
cessing with Asynchronous Memory Access.
• When more than one word is read from I/O memory using a communica-
tions command, the data contained in the words may not be concurrent.
• If an instruction reads more than one word of I/O memory and peripheral
servicing is executed during execution of the instructions, the data con-
tained in the words may not be concurrent.
• If the same word in I/O memory is read by more than instruction at differ-
ent locations in the program and peripheral servicing is executed between
execution of the instructions, the data contained in the word may not be
concurrent.
The following steps can be used to ensure data concurrency when required.
1. Use Parallel Processing with Synchronous Memory Access
2. Use the IOSP(287) to disable peripheral servicing for where required in the
program and then use IORS(288) to enable peripheral servicing again.
6-9 Peripheral Servicing Priority Mode
Peripheral servicing for RS-232C port, the peripheral port, the Inner Board
(CS Series only), CPU Bus Units, and Special I/O Units is normally serviced
only once at the end of the cycle after the I/O refresh. Either 4% of the cycle
time or a user-set time is allocated to each service. A mode, however, is avail-
able that enables periodic servicing within a cycle. This mode, called the
Peripheral Servicing Priority Mode, is set in the PLC Setup.
Note The Peripheral Servicing Priority Mode can be used with CJ-series CPU Unit
or CS-series CPU Units, but the CS-series CS1 CPU Unit must have a lot
number 001201@@@@ or later (manufacture date of December 1, 2000 or
later).
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