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3.9 Preset Multiple Registers (16)

This function is used for setting the value of a consecutive block of 16-bit

registers. Broadcast mode is allowed. Question.

In addition to the address of the slave and the function code (16), the

message contains the starting address, the number of words to be

written, the number of bytes that contain data and the data characters.

Address numbering starts from zero (word1 = 0) for MODBUS, from one

(word1 = 1) for JBUS.

NOTE: In the ATHENA CONTROLS implementation, this function is

present for compatibility but does not permit more than 8 word to be

assigned.

Example: Request to set 1 word to value 268 at address 35 on slave 17.

ADDR

FUNC

DATA

start

Addr HI

DATA

start

Addr LO

DATA

word #

DATA

word #

DATA

Byte

Count

DATA

word

35 HI

DATA

word

35 LO

CRC

11 10 00 22 00 01 02 01 0C 6C 87

Answer

In addition to the address of the slave and the function code (16), the

message contains the starting address and the number of words written.

Example: Answer to the request indicated above.

ADDR

FUNC

DATA

start

Addr HI

DATA

start

Addr LO

DATA

word #

DATA

word #

CRC

11 10 00 22 00 01 A3 53

4. Error Management

In MODBUS there are two types of errors, handled in different ways:

transmission errors and operating errors. Transmission errors are errors

that change the format of the message, the parity (if used) or the CRC16.

A device that detects errors of this type in the message treats it as invalid

and gives no answer. When the format of the message is correct but the

function requested cannot be executed for some reason, an operating

error has occurred. When it detects this kind of error, the slave device

answers by sending an error message. This message consists of the

address, the code of the function requested, an error code and the CRC.

To indicate that the answer is an error message, the function code is

returned with the most significant bit set to "1".

Example: Request for slave 10 to read bit 1185.

ADDR

FUNC

DATA

start

Addr HI

DATA

start

Addr LO

DATA

bit #

DATA

bit #

CRC

0A 01 04 A1 00 01 AC 63

Answer

The request is for the contents of bit 1185, which is not present on the

slave. The slave answers by sending error code "02" (ILLEGAL DATA

ADDRESS) and returns the function code 81h (129).

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 106 107

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