Omron SYSMAC C Series User Manual page 103

Scan time
Total execution time = 512 addresses X 14.75us = 7.55ms
Adding the four parameters provides the total scan time:
1.07ms + 1.04ms + 7.55ms + 1.1ms = 10.76ms
Notice that if no peripheral device is connected to the PC, the fourth
parameter in this equation is Oms.
Next, let's consider the scan time for a system that has a 56-point
expansion I/O unit connected and the user program consists of 1194
addresses. Again, it is assumed that only the LD and OUT instructions are
used in the program.
As before, there are two known factors: common process time and
peripheral device command servicing time, which are 1.07ms and 1.1ms,
respectively. The variable N of the equation for calculating the data
input/output time is 2 because a 56-point expansion I/O unit is used.
Therefore, the data input/output time is:
1.04ms + (0.33ms x 2) = 1.7ms
Because the program has 1194 addresses and uses only the LD and
OUT instructions, the total instruction execution time is:
1194 addresses x 14.75us = 17.61ms
Therefore, the scan time is:
1.07ms + 1.7ms + 17.61ms + 1.1ms = 21.48ms
Input/output response time of PC
Response time means the time from when the PC receives an input signal
until it outputs a control signal. This response time varies. If the PC
receives an input signal immediately after one scan time has finished and
if the input ON-delay time of the PC is minimum, the response time is
minimized. If those two factors exist, the response time can be obtained
by simply adding together the minimum input ON-delay, output ON-
delay, and scan times of the PC.
However, if the PC receives the input signal when one scan time has just
started and the input ON-delay time is the maximum value, the response
time is longer. This is because the CPU must wait until the end of the. `
preceding scan time before the input signal can be accepted. Therefore,
the maximum response time is the sum of the maximum input ON-delay,
output ON-delay, and two scan times.
The timing charts of the minimum and maximum response times required
for the PC to execute the following program are shown next.
C-5