Read Coil/Input Status (Function 01 / 02); Read Holding/Input Registers (Function 03 / 04); Table 27. Read Coil/Input Status (Modbus Function 01/02); Table 28. Read Holding/Input Registers (Modbus Function 03/04) - WEST P8700 User Manual

Read Coil/Input Status (Function 01 / 02)

Reads the content of instruments output/input status bits at the specified bit address.

Table 27. Read Coil/Input Status (Modbus Function 01/02)

Function
01 / 02
Function
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 28. Read Holding/Input Registers (Modbus Function 03/04)

Function
03 / 04
Function Number of
03 / 04
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.
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Address of 1st Bit
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Number of Bytes
Address of 1
HI
Bytes
HI
Modbus Communications
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-DIN & / - DIN Controllers & Indicators - Product Manual
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QUERY
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RESPONSE
First 8 bits
QUERY
st
Word
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RESPONSE
First Word
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Number of Bits
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2nd 8 Bits
Number of Words
HI LO
Last Word
HI
59305, Issue 5 – March 2005
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