West Control Solutions 8700+ - Manual (Page 129)

1 /
4
-DIN, 1 /
8
-DIN & 1 /
16
- DIN Controllers & Indicators - Product Manual
Page 124
Modbus Communications 59305, Issue 7 – March 2014
Read Coil/Input Status (Function 01 / 02)
Reads the content of instruments output/input status bits at the specified bit address.
Table 33. Read Coil/Input Status (Modbus Function 01/02)
QUERY
Function Address of 1st Bit Number of Bits
01 / 02 HI LO HI LO
RESPONSE
Function Number of Bytes First 8 bits 2nd 8 Bits
01 / 02
In the response the “Number of Bytes” indicates the number of data bytes read from the
instrument. E.g. if 16 bits of data are returned then the count will be 2. The maximum number
of bits that can be read is 16 in one transaction. The first bit read is returned in the least
significant bit of the first 8 bits returned.
Read Holding/Input Registers (Function 03 / 04)
Reads current binary value of data at the specified word addresses.
Table 34. Read Holding/Input Registers (Modbus Function 03/04)
QUERY
Function Address of 1
st
Word Number of Words
03 / 04 HI LO HI LO
RESPONSE
Function Number of
Bytes
First Word Last Word
03 / 04 HI LO HI LO
In the response the “Number of Bytes” indicates the number of data bytes read from the
instrument. E.g. if 5 words are read, the count will be 10 (A hex). The maximum number of
words that can be read is 64. If a parameter does not exist at one of the addresses read,
then a value of 0000h is returned for that word.