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6-2-1 Synchronous Operation
CVM1D PCs always operate in synchronous operation; the instruction execu-
tion processing and Programming Device servicing are synchronized in a
single cycle. The cycle time is thus the sum of the time required for instruc-
tion execution and that required for Programming Device servicing, and the
cycle time will lengthen as more Communications Units and Special I/O Units
are connected that are serviced during Programming Device servicing.
Instruction Execution Cycle Time
Process
Actions
Processing time
Basic processes
Checks the cycle time
and PC memory.
Checks the CPU bus,
PC memory, battery,
start input, duplex bus,
and updates the clock.
Duplex mode: approx. 8.5 ms
Simplex mode: approx. 5.0 ms
Event processing
Execution of non-scheduled requests for data
processing from Programming Devices.
0 ms if there is no processing request; 20 ms
max. (12% of previous cycle’s cycle time is for
servicing.)
Program
execution
Program executed.
For ladder programs, total execution time for all
instructions varies with program size, the
instructions used, and execution conditions.
Refer to 6-4 Instruction Execution Times for
details.
Output refreshing
Output terminals are updated according to
status of output bits in memory (including
Special I/O Units).
7
µ
s per word (per 16 points)
Input refreshing
Input bits are updated according to status of
input signals (including Special I/O Units).
8
µ
s per word (per 16 points)
SYSMAC BUS
refreshing
Input bits allocated to Units connected to Slaves
are updated according to status of input signals.
Output signals sent to Units connected to Slaves
are updated according to status of output bits in
memory.
1 ms per Master plus 0.05 ms per word on
Remote I/O Slaves (0.12 ms per word on Optical
I/O Units)
CPU Bus Unit
servicing
Refreshing and event processing are performed
in unit-number order starting with Unit #0.
(Refreshing involves only CPU Bus Link
refreshing of BASIC Units and Personal
Computer Units.)
SYSMAC NET Link/SYSMAC LINK refreshing:
Approx. 1.4 ms + 1
µ
s per data link word +
0.3 ms if both DM and CIO are used for data
links.
SYSMAC BUS/2 refreshing:
Approx. 2.0 ms + 1
µ
s per word refreshed
S
Approx. 0.8 ms for BASIC Unit refreshing
S
Approx. 0.8 ms for Personal Computer
S
Approx. 1 ms for event processing
Programming
Device servicing
If a Programming Device is connected,
commands from it are processed.
1.2 ms
Host interface
servicing (Pin 3 of
DIP switch OFF)
Host link servicing is processed if a host link is
connected to the DPL Unit.
1.2 ms
NT link servicing
(Pin 3 of DIP
switch ON)
The NT link is serviced when a PT is connected
to the CPU and the NT link is being used.
NT link servicing is processed if a PT is
connected to the DPL Unit and an NT link is
established.
Fixed at 2.2 ms
I/O bus check
Performs an I/O bus check of basic Racks.
1.2 ms
Duplex refreshing
(Duplex mode
only)
Transfers input refreshing data to the standby
CPU Unit.
10
µ
s per Input Unit word
The Service Disable Bits shown in the table below are primarily used to reduce
the cycle time; they are only effective in RUN and MONITOR modes. The bits are
OFF when the PC is first turned on, and are normally turned ON from the pro-
gram.
Service Disable Bits
Cycle Time
Section 6-2
Summary of Contents for CVM1D
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