Varec 4000 manual Status Bits, Status Bit Data, Exception Responses, Exception Response Reason

4000 Modbus Implementation

9.7Status Bits

In the ATT implementation, status bits contain alarms, commands, and status information. The state of a Modbus status bit is defined as either ON (true) or OFF (false). The ON state is represented by a "1". The status bits may be read with function code 1 or 2. They may be written one at a time with function code 5 or multiple bits may be written with function code 15. An example of a read message for bits 2 through 6 as returned by the ATT is shows as follows.

Host Request

Address	Function	Start Reg	Start Reg	# of Reg	# of Reg	Error
	Code	H	L	H	L	Check
01	02	00	02	00	04	XX
ATT Response
Address	Function	Byte	Data	Error
	code	Count		Check
01	02	01	12	XX

9.7.1Status Bit Data

Binary representation 1 0010 (bits 6-2)

Bit #2: High Advisory Alarm OFF

Bit #3: High Critical Alarm ON

Bit #4: Unauthorized Mass Movement OFF

Bit #5: Standard Density Alarm OFF

Bit #6: Critical Zone Alarm ON

9.8Exception Responses

The exception responses returned by the ATT are listed below:

Exception	Response	Reason
01	Illegal Function	Message is not allowed
02	Illegal Data Address	Data address (bit or register) requested is not defined
03	Illegal Data Value	Data value being written is out of range
04	Busy	During power-up

In addition, messages that are received with a parity error, checksum error, or message format error will be ignored.

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