O
PEN
N
ET
C
ONTROLLER
U
SER
’
S
M
ANUAL
21-1
21: D
ATA
L
INK
C
OMMUNICATION
Introduction
This chapter describes the data link communication function used to set up a distributed control system.
A data link communication system consists of one master station and a maximum of 31 slave stations, each station com-
prising an
OpenNet Controller
CPU module and I/O modules. When the data link communication is enabled, the master
station has 20 data registers assigned for each slave station, and each slave station has 20 data registers for communication
with the master station. Using these data registers, the master station can send and receive data of 10 data registers to and
from each slave station. Any particular program is not required for sending or receiving data in the data link communica-
tion system.
When data of inputs, outputs, internal relays, timers, counters, or shift registers are moved to data registers using the move
instructions in the user program, these data can also be exchanged between the master and slave stations.
The
MICRO
3
,
MICRO
3
C
, FA-3S series PLCs and HG2A series operator interfaces can also be connected to the data link
communication system.
Data Link Specifications
Electric Specifications
Compliance with EIA-RS485
Baud Rate
19,200 or 38,400 bps
Synchronization
Star t-stop synchronization
Star t bit:
1
Data bits:
7
Parity:
Even
Stop bit:
1
Communication Cable
Shielded twisted pair cable, core wire diameter 0.9 mm (0.035”) minimum
Maximum Cable Length
200m (656 feet) total
Maximum Slave Stations
31 slave stations
Refresh Mode
Separate or simultaneous refresh
Transmit/Receive Data
0 through 10 words each for transmission and receiving per slave station
Special Internal Relay
M8005-M8007:
communication control and error
M8140-M8176:
communication completion for each slave station
M8177:
communication completion for all slave stations
Data Register
D7000-D7619 for transmit/receive data
Special Data Register
D8400-D8430 for communication error code
Communication
Selector
DIP Switch
Master Station
Slave Station 1
Slave Station 2
HG Series
Operator
Interface
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Slave Station 31
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: [email protected]
