Publication 1762-RM001C-EN-P
MicroLogix 1200 Memory Usage and Instruction Execution Time A-7
MicroLogix 1200
Scan Time Worksheet
Calculate the scan time for your control program using the worksheet
below.
Communications Multiplier Table
Input Scan (sum of below)
Overhead (if expansion I/O is used) = 55 µs
Expansion Input Words X 10 µs (or X 14 µs if Forcing is used) =
Number of modules with Input words X 80 µs =
Input Scan Sub-Total =
Program Scan
Add execution times of all instructions in your program when executed true =
Program Scan Sub-Total =
Output Scan (sum of below)
Overhead (if expansion I/O used)
= 30 µs
Expansion Output Words X 3 µs (or X 7 µs if Forcing is used) =
Output Scan Sub-Total =
Communications Overhead
(1)
Worst Case =1470 µs
Typical Case = 530 µs
Use this number if the communications port is configured, but not communicating to
any other device.
= 200 µs
Use this number if the communications port is in “Shutdown” mode. = 0 µs
Communications Overhead Sub-Total =
System Overhead
Add this number if your system includes a 1762-RTC or 1762-MM1RTC. = 100 µs
Housekeeping Overhead = 270 µs
System Overhead Sub-Total =
Totals
Sum of all sub-totals
Multiply by Communications Multiplier from Table X
Total Estimated Scan Time =
(1) Communications Overhead is a function of the device connected to the controller. This will not occur every scan.
Protocol
Multiplier at Various Baud Rates
38.4K 19.2K 9.6K 4.8K 2.4K 1.2K 600 300
Inactive
(1)
DF1 Full-Duplex 1.50 1.27 1.16 1.12 1.10 1.09 1.09 1.08 1.00
DF1 Half Duplex Slave 1.21 1.14 1.10 1.09 1.08 1.08 1.08 1.07 1.01
DH-485 N/A 1.16 1.11 N/A N/A N/A N/A N/A 1.10 at 19.2K
1.07 at 9.6K
Modbus™ 1.22 1.13 1.10 1.09 1.09 1.09 1.09 1.09 1.00
Shut Down 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
(1) Inactive is defined as No Messaging and No Data Monitoring. For DH-485 protocol, inactive means that the controller is not connected to a network.
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