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