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Despatch P1400+ Temperature Controller User Manual

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Read Coil/Input Status (Function 01 / 02)

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

Table 17.

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 18.

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.