Omega CN1166 B. Read Holding Registers Read n Words 03/04, C. Force Single Coil Write 1 Bit, Addr

This function will be used largely to report controller status information, and so a bit set to 1 indicates that the corresponding feature is currently enabled/active, and a bit reset to 0 indicates the opposite.

If an exact multiple of eight bits is not requested, the data is padded with trailing zeros to preserve the 8-bit format. After the data has been transmitted, the CRC16 value is sent.

B. Read Holding Registers (Read n Words) 03/04

The message sent to the controller to obtain the value of one or more registers is an eight-byte message as follows:

		Addr. of
Addr.	Func.	1st Word		No. of words		CRC16
	3/4	HI	LO	HI	LO	HI	LO

The reply sent by the controller echoes the first 2 characters received and then contains a single-byte data byte count, the value of which does not include either itself or the CRC value to be sent. For this message, the count equals the number of parameters read times two. Following the byte count, that number of parameter values are transmitted, MSB first, followed by the CRC16.

Addr.	Func.	Count	1st value		2nd value
	3/4		HI	LO	HI	LO

	Last value		CRC16
	HI	LO	HI	LO
C. Force Single Coil (Write 1 Bit)			05	B

The message received by the controller is 8 bytes long, consisting of the standard preamble and the address of the bit to force, followed by a two-byte word whose MSB contains the desired truth value of the bit expressed as 0xFF (TRUE) or 0x00 (FALSE).

Addr.	Func.	Addr. of Bit		State		CRC16
	5	HI	LO	FF/00	0	HI	LO

Generally, this function will be used to control such features as Auto/Manual and Tuning.

The normal reply sent by the controller will be a byte-for-byte echo of the message received.

O077-4 Volume II 4-3