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The first three operations immediately after power application are performed
only once each time the PC is turned on. The rest of the operations are per-
formed in cyclic fashion. The cycle time is the time that is required for the CPU to
complete one of these cycles. This cycle includes basically eight types of opera-
tion.
1, 2, 3...
1. Overseeing
2. Program execution
3. Cycle time calculation
4. I/O refreshing
5. Host Link Unit servicing
6. RS-232C port servicing
7. Peripheral Device servicing
8. SYSMAC NET/SYSMAC LINK servicing.
The cycle time is the total time required for the PC to perform all of the above
operations. The time required for operation 3, cycle time calculation, is negligi-
ble and can be ignored in actual calculations
Operation Time required Function
1. Overseeing 0.7 ms Watchdog timer set. I/O Bus, Program
Memory checked. Clock refreshed.
2. Program
execution
Total execution time for all instructions varies
with program size, the instructions used, and
execution conditions. Refer to
6-3 Instruction
Execution Times
for details.
Program executed.
3. Cycle time
calculation
Negligible, but a wait can be generated to
bring the cycle time up to the minimum set-
ting if one has been made.
Cycle time calculated. When the CYCLE
TIME instruction (SCAN(18)) is executed,
waits until the set time has elapsed and
then resets the watchdog timer.
4. I/O refreshing Total of following times:
20
µs per input byte (8 points). 20 µs per
output byte. (12-point Output Units calcu-
lated as 16 points.)
PC Link Unit I/O refresh time.
Special I/O Unit refresh time.
1.1 ms per Remote I/O Master Unit +
0.17 ms per I/O word used on Slave Racks.
Group-2 (High-density) I/O Unit refresh time.
Refer to the tables below for details on PC
Link, Special I/O Unit, and Group-2 High-
density I/O Unit refresh times.
Input bits set according to status of input
signals. Output signals sent according to
status of output bits in memory.
Inputs and Outputs in Remote I/O Systems
refreshed.
Special I/O Units serviced.
Group-2 High-density I/O Units serviced.
5. Host Link Unit
servicing
6 ms per Unit max. Commands from computers connected
through Rack-mounting Host Link Units
processed.
6. RS-232C port
servicing
(except CPU01-E/03-E)
0 ms when no device is connected.
T x 0.05, where T is the cycle time calculated
in operation 3
Communications with devices connected
to RS-232C port processed.
7. Peripheral device
servicing
0 ms when no device is connected.
0.26 ms minimum or T x 0.05, where T is the
cycle time calculated in operation 3
Commands from Programming Devices
(computers, Programming Consoles, etc.)
processed.
8. SYSMAC NET/
SYSMAC LINK
servicing
(CPU31-E/33-E only)
0 ms when no Communications Unit is
mounted.
0.8 ms + 10 ms max. per Unit.
Commands from computers and other de-
vices connected to SYSMAC NET/SYS-
MAC LINK Units processed.
Cycle Time Section 6-1