Hitachi EH-150 Series Applications Manual page 175

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