71
C1000H and C2000H Systems
Section 6-3
Calculations would be as shown below for input and output ON delays of
10 ms and a scan time of 20 ms. This example uses only one Slave Rack
connected to a Master and four words allocated on the Slave Rack. Because
there is only one Slave, T
RM
and T
RT
are the same.
T
RT
=
1.4 + (0.2 x 4) = 2.2 ms
T
RM
= 2.2
ms
Minimum I/O Response Time
Time = 10 ms + 20 ms + 2.2 ms + 10 ms
= 42.2 ms
Maximum I/O Response Time
Time = 10 ms + (20 ms x 2) + (2.2 ms x 2) + 2.2 ms + 10 ms
= 66.6 ms
The above computations assume that there is no remote I/O error (including
power interruptions). If an error occurs for a Slave, the response time would
be increased by 20 ms for each Slave connected to the same Master as the
Slave where the error occurred. If an error occurs for a Remote Terminal, the
overall delay time would be increased by 5 ms for each Remote Terminal
connected to the same Master as the Remote Terminal where the error oc-
curred.
6-3
C1000H and C2000H Systems
With C1000H and C2000H Remote I/O Systems, both the scan time of the
PC and the transmission time required by the Remote I/O System need to be
considered in computing the I/O response times.
The remote I/O transmission time is computed as follows:
T
RM
=
Total Slave transmission time for one Master
=
Σ
T
RT
+ T
TT
T
RT
= Transmission time for each Slave
= 1.4 ms + (0.2 ms x n)
Where n = number of I/O words on the Slave Rack
T
TT
= Remote Terminal transmission time
= 0.2 ms x m
Where m = number of Remote Terminals
The minimum response time occurs when all signals are processed as soon
as they are received. Because remote I/O processing is handled in parallel
with program execution, two scans are required so that the program is ex-
ecuted.
Time = Input ON delay + (scan time x 2) + (T
RT
or T
TT
) + output ON delay
The maximum response time occurs when the input just misses both the first
remote I/O transmission and the program execution portion of the scan,
meaning that processing must wait for the next transmission and then the
next (i.e., the third) scan.
Time = Input ON delay + (scan time x 3) + (T
RM
x 2) + (T
RT
or T
TT
) + output
ON delay
Example Computations
Transmission Time for
Remote I/O Errors
Remote I/O Transmission
Times
Minimum I/O Response
Times
Maximum I/O Response
Times
