5. SETTINGS BEFORE OPERATION
IMS01J02-E4
51
RS-485 (2-wire system) send/receive timing
The sending and receiving of RS-485 communication is conducted through two wires; consequently,
the transmission and reception of data requires precise timing. Typical polling and selecting
procedures between the host computer and SR Mini HG SYSTEM are described below:
Polling procedure
a
: Response send time after SR Mini HG SYSTEM receives [ENQ]
Interval time
b
: Response wait time after SR Mini HG SYSTEM sends BCC
c
: Response send time after SR Mini HG SYSTEM receives [ACK]
Interval time or
Response send time after SR Mini HG SYSTEM receives [NAK]
Interval time
Selecting procedure
a:
Response send time after SR Mini HG SYSTEM receives BCC
Interval time
b:
Response wait time after SR Mini HG SYSTEM sends ACK or
Response wait time after SR Mini HG SYSTEM sends NAK
To switch the host computer from transmission to reception, send data must be on line. To
check if data is on line, do not use the host computer’s transmission buffer but confirm it by
the shift register.
Whether the host computer is using either the polling or selecting procedure for
communication, the following processing times are required for SR Mini HG SYSTEM to
send data:
-Response wait time after SR Mini HG SYSTEM sends BCC in polling procedure
-Response wait time after SR Mini HG SYSTEM sends ACK or NAK in selecting
procedure
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.
Send data
(Possible/Impossible)
Host computer
- - - - -
Possible
Impossible
or
Sending status
SR Mini HG
SYSTEM
Possible
b c
a
Impossible
- - - - -
Send data
(Possible/Impossible)
Sending status
N
A
K
A
C
K
E
N
Q
S
T
X
B
C
C
E
O
T
Possible
Impossible
or
Possible
b
a
Impossible
- - - - -
Send data
(Possible/Impossible)
Host computer
Sending status
SR Mini HG
SYSTEM
Send data
(Possible/Impossible)
Sending status
S
T
X
B
C
C
N
A
K
A
C
K
