APPENDIX. HOST COMMUNICATION PROTOCOL
IMR02E20-E1
111
RS-485 (2-wire system) send/receive timing
RS-485 communication is conducted through two wires, therefore the transmission and reception of
data requires precise timing.
Polling procedure
a: Response send time after the controller receives [ENQ] + Interval time
b: Response send time after the controller sends BCC
c: Response send time after the controller receives [ACK] + Interval time or
Response send time after the controller receives [NAK] + Interval time
- - - - -
or
Host
computer
b
c
a
- - - - -
N
A
K
A
C
K
E
N
Q
S
T
X
B
C
C
E
O
T
SRZ unit
Send data
(Possible/Impossible)
Possible
Impossible
Sending status
Send data
(Possible/Impossible)
Possible
Impossible
Sending status
Selecting procedure
a: Response send time after the controller receives BCC + Interval time
b: Response wait time after the controller sends ACK or Response wait time after the controller sends NAK
b
a
- - - - -
S
T
X
B
C
C
or
N
A
K
A
C
K
Host
computer
SRZ unit
Send data
(Possible/Impossible)
Possible
Impossible
Sending status
Send data
(Possible/Impossible)
Possible
Impossible
Sending status
To switch the host computer from transmission to reception, send data must be on line.
The following processing times are requires for the SRZ unit to process data.
- In Polling procedure, Response wait time after the SRZ unit sends BCC
- In Selecting procedure, Response wait time after the SRZ unit sends ACK or NAK
Fail-safe
A transmission error may occur with the transmission line disconnected, shorted or set to the
high-impedance state. In order to prevent the above error, it is recommended that the fail-safe function
be provided on the receiver side of the host computer. The fail-safe function can prevent a framing
error from its occurrence by making the receiver output stable to the MARK (1) when the transmission
line is in the high-impedance state.
