RKC INSTRUMENT PG500, Инструкция по эксплуатации системы связи

Страница: 23 / 70

2. HOST COMMUNICATION
IMR02F04-E1
17

RS-485 (2-wire system) send/receive timing (RKC communication)
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 PG500 receives [ENQ] + Interval time
b: Response send time after the PG500 sends BCC
c: Response send time after the PG500 receives [ACK] + Interval time or
Response send time after the PG500 receives [NAK] + Interval time

Selecting procedure
a: Response send time after the PG500 receives BCC + Interval time
b:
Response wait time after the PG500 sends ACK or Response wait time after the PG500 sends NAK
To switch the host computer from transmission to reception, send data must be on line.
The following processing times are required for the PG500 to process data:
- In polling procedure, Response wait time after the PG500 sends BCC
- In selecting procedure, Response wait time after the PG500 sends ACK or NAK

Fail-safe
A transmission error may occur if the transmission line is 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.
or
b
a
Send data
(Possible/Impossible)
Possible
Impossible
Sending status
Host
computer
PG500
Possible
Impossible
Send data
(Possible/Impossible)
Sending status
- - - - -
S
T
X B
C
C
N
A
K A
C
K
Send data
(Possible/Impossible)
- - - - -
Possible
Impossible
or
Sending status
Host
computer
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
PG500