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Modbus RTU Function Codes

02/13 Modbus® RTU Serial Communications User Manual 21

3.7 Function Codes 16 (10h) – Preset Multiple Registers

Description

Presets values into a sequence of holding registers (4X references). When broadcasted, the function presets

the same register references in all attached slaves.

The specific supported registers available in an instrument via a Function Code 16 (10h) message may be

instrument-model specific. However, every instrument that supports the register assignments specified in

Appendix A with an access type “W”, supports writing to those specified registers via Function Code 16

(10h).

Query

The query message specifies the register references to be preset. Registers are addressed starting at zero:

Query message format for function code 16 (10h)

Slave

Address

Function

Code

Starting

Address

High

Start

Address

Low

Number

Addresses

High

Number

Addresses

Low

Byte

Count

Data CRC CRC

Example:

Preset Variable#1 (address 1880h) to 100.0 from a slave at address 02.

02 10 18 80 00 02 04 42 C8 00 00 CRC CRC

Response

The normal response returns the slave address, function code, starting address and the quantity of registers

preset.

The floating-point values require two consecutive addresses. A request to preset a single floating-point

value must be for two addresses. The byte order of the floating-point number is determined by the setting of

the byte swap configuration value. In this example the byte swap order is FP B. Refer to subsection 2.3. The

first 16 bits of the response contain the IEEE MSB of the float value. The second 16 bits of the response

contain the IEEE LSB of the float value. The Byte order is configurable See Subsection 0. If the master

station requests only one address at an address of a floating-point value the slave will respond with an illegal

data address exception (See Section 4) code.

Response message format for function code 16 (10h)

Slave

Address

Function

Code

Starting

Address

High

Start

Address

Low

Number

Addresses

High

Number

Addresses

Low

CRC CRC

Example:

Response from preset Constant #1 (address 1880h) to 100.0 from a slave at address 02.

02 10 18 80 00 02 CRC CRC

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 75 76

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