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2 Simple Application Controllers
The Command String 7
7 - 6
7.3.1 Control Codes
The Control codes are listed below:
7.3.2 No. of Communication Bytes
The number of communication bytes is used to check the validly of the message syntax. When
using Format A the number of communication bytes for the Transmit message starts from the
Format No. and finishes with the ENQ control code. The number of communication bytes for a
Receive message starts from the Format No. and finishes with the ACK control code. In the
situation of receiving an error message the number of communication bytes for a Receive
message starts from the Format No. and finishes with the appropriate error code.
Format A Type - Line Check
Table 7.4: Control Codes
Signal
Code
(Hex)
Description
STX 02H
S
tart of
T
e
X
t
ETX 03H
E
nd of
T
e
X
t
ENQ 05H
ENQ
uiry
ACK 06H
ACK
nowledge
NAK 15H
N
egative
A
c
K
nowledge
! 21H Completion
Computer
α
2 Controller
03 = 01 + 01 + 01
03 = 01 + 01 + 01 (bytes)
04 = 01+01 + 01 (bytes)+01
or
S
T
X
A
C
K
Format No.
Station No.
S
T
X
N
A
K
Format No.
Station No.
Error Code
S
T
X
E
N
Q
Format No.
Station No.
No. comm
bytes
03H
No. comm
bytes
03H
No. comm
bytes
04H
(bytes)