2.9 Anatomy of a Message Packet
Symbol key:
Symbol
DLE
STX
ETX
DADR
SADR
SEQ
CRC
ANAK
AACK
ERRCODE
Host to Instrument
DLE|STX|DADR|SADR|SEQ|...message*...|CRC|CRC|DLE|ETX
Instrument to Host
(1) If message was good and the instrument understood the message
DLE|STX|DADR|SADR|SEQ|...message*...|CRC|CRC|DLE|ETX
(2) If message was good but the instrument rejected the message (i.e. application level failure)
DLE|STX|DADR|SADR|SEQ|ANAK|ERRCODE
(3) If message was bad
Silence.
8/99
Value
Meaning
0x01
Precedes control characters.
0x02
Start of transmission.
0x03
End of transmission.
Destination address.
1
Controller
0xff
Host
Source address.
1
Controller
0xff
Host
n/a
Sequence number.
n/a
Cyclic redundancy check.
0x09
Application level negative acknowledge
0x0a
Application level acknowledge.
n/a
Error code explaining why instrument rejected message.
(See Subsection 2.11- Table 2-1)
*
Refer to Section 4 - Message Exchange Formats
*
Refer to Section 4 - Message Exchange Formats
RS232 Communications Reference Manual
Protocol Description
|CRC|CRC|DLE|ETX
(see table 2-1)
5