Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 153)

Publication AG-UM008C-EN-P - February 2005
Configuring SLC 5/03, 5/04, and 5/05 Processors 4-15
Finally, you must determine the larger of two values, either the
configured slave RTS Send Delay or the turnaround time of the slave
modem. The RTS Send Delay time can be found by double-clicking
on the slave’s Channel Configuration icon and looking at the Chan. 0
System tab of the Channel Configuration screen. Note that the RTS
Send Delay time is in intervals of 20 ms, so with a value of 3 in the
box, the RTS Send Delay time would be 20 ms multiplied by 3. Using
this value (60 ms) for our example, and assuming that the turnaround
time of the modem is 50 ms (which will vary by modem), you would
choose to use the RTS Send Delay time of 60 ms for your calculation.
Having determined the maximum message transmission time (224
ms), the average slave program scan time (20 ms) and the largest of
either RTS Send Delay (60 ms) or the modem turnaround time, the
minimum ACK timeout is simply the sum of these values.
Parameter Example Values (in ms)
Max message transmission
time 224
Average program scan time 20
RTS Send Delay 60
modem turnaround time 50
calculated ACK Timeout 304
round up to nearest 20 ms 320
Use only the largest of these two values.