7-58
7-9-6 Communications Response Time
The communications response times for communications with an Inverter via the
RS-422/485 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-422/485 communications can be created using the
protocol macro 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 fol-
lowing formula.
Communications time = [No. of bytes in DSR message
´
10 (see note 1)
´
(1/baud
rate)
´
1,000 (ms)] + [No. of bytes in response
´
10
´
(1/baud rate)
´
1,000 (ms)] + [24
´
(1/baud rate)
´
1,000 (ms)] + send wait time setting n156 (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 mul-
tiplied 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-422/485 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
7-9-7
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. Conse-
quently, 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 communica-
tions errors, or increase the number of Masters thereby decreasing the number of
Slaves per Master.
Communications
Chapter 7
Summary of Contents for SYSDRIVE 3G3MV A2002
Page 1: ...USER S MANUAL SYSDRIVE 3G3MV Multi function Compact Inverter Cat No I527 E2 02...
Page 15: ...Chapter 1 Overview 1 1 Function 1 2 Nomenclature 1 3 New Features 1...
Page 24: ...Chapter 2 Design 2 1 Installation 2 2 Wiring 2...
Page 89: ...Chapter 4 Test Run 4 1 Procedure for Test Run 4 2 Operation Example 4...
Page 286: ...Chapter 9 Specifications 9 1 Inverter Specifications 9 2 Option Specifications 9...
Page 311: ...Chapter 10 List of Parameters 10...
Page 342: ...Chapter 11 Using the Inverter for a Motor 11...
Page 348: ...Appendix A Standard Models...