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J
Transmission
procedure
Host computer
H8GN
J
Interface
J
Wiring
Host computer
RS 485
Abbr
FG
-
+
SG
A<B: [1] mark
A>B: [0] space
Both ends of the transmission line
(including the host computer) must be
specified (by setting terminator ON) as
the end node. The total resistance of
the terminators must be at least 54
When the host computer transmits a command frame, the H8GN trans
mits a response frame that corresponds to the command frame. A single
response frame is returned for each command frame. The following dia
gram shows the operation of the command and response frames.
Command frame
Allow a wait time of at least 2 ms until the next command is sent after the
host computer receives a response from the H8GN.
Communications with the host computer are carried out through a stan
dard RS 485 interface.
•
RS 485 connections can be 1 : 1 or 1 : N. A maximum of 32 Units (including
the host computer) can be connected in one to N systems.
•
The total cable length is 500 m max.
•
Use a shielded, twisted pair cable AWG28 or larger for wiring the H8GN.
Shielded cable
Ω
Shielded cable
.
Match the communications specifications of the H8GN and the host com
puter. If a one to N system is being used, be sure that the communications
specifications of all devices in the system (except individual unit numbers)
are the same.
Command frame
Response frame
Communications transceiver
H8GN
RS 485
Pin No.
Abbr
8
A(-)
7
B(+)
6.8V
Terminator
H8GN
Ω
120
end node
(1/2W)
RS 485
Pin No.
Abbr
8
A(-)
7
B(+)
Use a terminator of resistance
Ω
120
= (1/2W).
1.1 Outline
TX
RX
1-3
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