8
Request
Instrument
Address
Function
(16)
Starting
Address
Word Count Byte Count
1 byte
1 byte
2 bytes
2 bytes
1 byte
Data Word 1
...
...
...
Data Word N
Error Check
2 bytes
...
...
...
2 bytes
2 bytes
Starting Address
Address of the first register to be written
Word Count
The number of contiguous words to be written
Byte Count
The number of bytes to be written
Response
Instrument
Address
Function
(16)
Starting
Address
Word
Count
Error
Check
1 byte
1 byte
2 bytes
1 word
2 bytes
3.5 Function 08 - Loop-back Communications Test
The purpose of this request is to check the communications link between the specified instrument and PC.
Request
Instrument
Address
Function
(08)
Diagnostic
Code (0)
Data
Error
Check
1 byte
1 byte
2 bytes
2 bytes
2 bytes
Diagnostic Code
Designates action to be taken in Loop-back test. The protocol supports only Diagnostic Code
0 - return query data.
Data
Query data. The data passed in this field will be returned to the master through the
instrument. The entire message returned will be identical to the message transmitted by the
master, field-per-field.
Response
Instrument
Address
Function
(08)
Diagnostic
Code (0)
Data
Error
Check
1 byte
1 byte
2 bytes
2 bytes
2 bytes
The normal response is the re-transmission of a test message.
3.6 Exception Responses
The instrument sends an exception response when errors are detected in the received message. To indicate that
the response is notification of an error, the high order bit of the function code is set to 1.
Exception Response
Instrument
Address
Function (high order
bit is set to 1)
Exception
Code
Error Check
1 byte
1 byte
1 byte
2 byte
Exception response codes:
01
- Illegal
function
02
- Illegal data address
03
- Illegal data value
06
- Busy, rejected message. The message was received without errors, but the instrument is being
programmed from the keypad (only for requests accessing setup registers).
NOTE
When the character framing, parity, or redundancy check detects a communication error, processing of
the master's request stops. The instrument will not act on or respond to the message.
