TOHO ELECTRONICS TRM-006A - Manual (Page 20)

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6. MODBUS communications control
6.1 Communications procedure
This product returns a "response message" in response to a "request message" from a high-level
computer. It therefore does not initiate a transmission.
High-level computer
This product
Request message
Response message
Request message
Response message
Transmitted by a high-
level computer
Transmitted by this
product
Transmitted by a high-
level computer
Transmitted by this
product
1ms or more, or 3.5 character seconds or more,
whichever the longer Response delay:
0-250ms
See "5.8 Setting a response delay."
See "6.6.1 Communications timing." See "6.6.2 Interval between requests."
6.2 Message types
n Messages are roughly divided into the following types:
Read request message
Write request message
Store request message
Request message (transmitted
from a high-level computer)
Response message (transmitted
from this product)
Receipt acknowledgement and data
response
Write complete response
Reception error and error description
response
Store complete response
: Response when a normal "request message" is received
: When a received "request message" contains an error
n In RTU codes, the data is binary.
n In ASCII codes, all codes are expressed in ASCII codes.
n In assembling a program for a high-level computer, see "9. Table of identifiers (codes)" and "10.
Table of ASCII codes" at the end of the book.