Micromod MOD: Modcell 2050R MODBUS Communications - Manual (Page 37)

IB-23C650M
MODBUS PROTOCOL
MODBUS PROTOCOL
Communications Speed
The controller supports baud rates of 150, 300, 1200, 2400, 4800, 9600, 19.2K,
and 38.4K baud. Messages are not buffered. A new message (including
broadcast type) will not be accepted until an existing message has been
processed and responded to if necessary.
Message Response Time
The controller typically takes between 10 and 30 milliseconds to respond to a
message requesting 10 registers. This time is from the end of the request
message to the start of the response message.
The total amount of time a message takes to get back and forth between the
host and the slave depends on the message size, baud rate and the slave's
time to process the message. The following information is for a request
message to read 10 registers:
• request message size is 8 characters + 3.5 idle time characters (11.5).
• response message size is 25 characters + 3.5 idle time characters (28.5).
• for this example, a character is 11 bits (1 start, 8 data, 1 parity, 1 stop).
• Therefore, the total typical time using a controller response time of 30
milliseconds is shown below for the various baud rates:
Baud Rate
Request Time
(mSec)
Response
Time (mSec)
Total Typical
Time (mSec)
150 623 2090 2743
300 312 1045 1387
1200 78 261 369
2400 39 131 190
4800 19 65 114
9600 10 33 73
19200 5 16 51
38400 2 8 40
33