West Control Solutions N8100 - Manual (Page 28)

3.2.3 Communications Protocol
The protocol assumes half duplex communications. All communication is initiated
by the master device. The master sends a command or query to the addressed
slave and the slave replies with an acknowledgement of the command or the
reply to the query. All messages, in either direction, comprise:
(a) A Start of Message character
(b) One or two address characters (uniquely defining the slave)
(c) A parameter/data character string
(d) An End of Message character
Messages from the master device may be one of four types:
Type 1: L {N} ? ? *
Type 2: L {N} {P} {C} *
Type 3: L {N} {P} # {DATA} *
Type 4: L {N} {P} I *
where all characters are in ASCII code and:
L is the Start of Message
character (Hex 4C)
{N} is the slave Controller
address (in the range 1 -
32); addresses 1 - 9 may be
represented by a single digit
(e.g. 7) or in two-digit form,
the first digit being zero (e.g.
07).
{P} is a character which identifies the parameter to be
interrogated/modified.
{C} is the command (see below)
# indicates that {DATA} is to follow (Hex 23)
{DATA} is a string of numerical data in ASCII code (see Table 3-1)
* is the End of Message character (Hex 2A)
No space characters are permitted in messages. Any syntax errors in a received
message will cause the slave controller to issue no reply and await the Start of
Message character.
3-2 O054-3
59125
{DATA} Content Sign/Decimal Point
abcd0 +abcd
abcd1 +abc.d
abcd2 +ab.cd
abcd3 +a.bcd
abcd5 -abcd
abcd6 -abc.d
abcd7 -ab.cd
abcd8 -a.bcd
Table 3-1 {DATA} Element - Sign
and Decimal Point