Communications Response Time - Omron SYSDRIVE 3G3JV User Manual

Communications

7-10-6 Communications Response Time

The communications response times for communications with an Inverter via the RS-422A/485 port of
an OMRON-made Communications Board are detailed below. Use this information as a reference
when deciding the number of Slaves to be connected to one network, and when considering the timing
of input and output signals.
H Communications Time for One Message
• A wide variety of programs for RS-422A/485 communications can be created using the protocol mac-
ro function. The communications times will vary according to the contents of the program.
• In general, the communications time for one message can be calculated using the following formula.
Communications time = [Number of bytes in DSR message × 10 (See note 1.) × (1/baud rate) ×
1,000 (ms)] + [Number of bytes in response × 10 × (1/baud rate) × 1,000 (ms)] + [24 × (1/baud rate) ×
1,000 (ms)] + send wait time setting n73 (ms) + protocol macro waiting time (See note 2.) (ms)
Note 1. The reason that the number of bytes in the DSR message and response is multiplied by 10 is
because both the start bit and the stop bit require one bit each.
(1 byte = 8 bits) + (start bit: 1 bit) + (stop bit: 1 bit) = 10 bits
Note 2. With RS-422A/485 communications, set at least 20 ms as the protocol macro waiting time.
D Calculation Example
The communications time required for one Slave in the protocol macro created in 7-10-4 Creating a
Project File, can be calculated according to the following formula. (Baud rate = 19,200 bps.)
Communications time = [(DSR message to write data (13 bytes) + DSR message to read (8 bytes))
× 10 × (1/19,200) × 1,000 (ms)] + [(write response (8 bytes) + read response (7 bytes)) × 10 ×
(1/19,200) × 1,000 (ms)] + [24 × (1/19,200) × 1,000 (ms) × 2] + [10 (ms) × 2] + [20 (ms) × 2] =
81.2 (ms)
Note If there are N Slaves, the total communications time will be N × 81.2 ms. Consequently, the more
Slaves that are used, the longer the communications time will be. If the number of Slaves is too
high, it is possible that the detection time of 2 s for communications time-over will be exceeded. In
this case, either disable the time-over detection function and use a different sequence to detect
communications errors, or increase the number of Masters thereby decreasing the number of
Slaves per Master.
H I/O Response Time
• The communications processing times for the Inverter are as follows.
S Inverter communications input scan: 8 ms
S Inverter communications output scan: 8 ms
S Internal processing time for the Inverter: Approx. 20 ms
• The I/O response times for the Inverter are illustrated in the following diagram.
Ladder program cycle time
Communications time × 2
Inverter I/O scan
Internal processing for
the Inverter
7-54
Max. output re-
Max. input re-
sponse time
sponse time
Chapter 7