Hitachi EH-150 Series - Page 175

Appendix
A - 11
If PLC cannot execute properly a request from a host, PLC returns a negative response NAK.
R
T
C
C
R
*RTC : Return code
Host
PLC
NAK
T
M
LUMP
Task
code
S
u
m
S
T
X
C
R
Figure.A.7 Transmission control procedure 1 Communication sequence diagram (Abnormal 1)
R
T
C
C
R
*RTC : Return code
Host
PLC
NAK
T
M
Task code
S
u
m
S
T
X
C
R
Figure.A.8 Transmission control procedure 2 Communication sequence diagram (Abnormal 1)
Table.A.8 Return code list
No.
RTC
Error factor
Priority
1
03
Framing error
High
2
01
Parity error
3
04
Over-run error
4
07
Receiving buffer error
5
08
Receiving time-out error
6
05
Protocol error
7
06
ASCII error
8
02
Sum error
Low
If a request includes invalid parameter (Illegal sub command or non existing I/O address, etc), PLC returns a task
code with error information such as task code error or not executed.
Response : Task code error or
Not executed
Host
PLC
ACK
T
M
LUMP
Task
code
S
u
m
S
T
X
C
R
ENQ
1
S
T
X
Res-
ponse
LUMP
C
R
Figure.A.9 Transmission control procedure 1 Communication sequence diagram (Abnormal 2)
Response : Task code error or
Not executed
Host
PLC
T
M
Task
code
S
u
m
S
T
X
C
R
S
T
X
Response
C
R
Figure.A.10 Transmission control procedure 2 Communication sequence diagram (Abnormal 2)