Octagon PC-500, User Manual

Page: 69 / 233

5-10
Serial ports PC-500 user’s manual
Table 5-14 RS-485 transmitter control: COM5 at location 320h
Program statement Description
A '1' in bit position 1, register
offset 4
Enables the transmitter function and
disables the receiver function
A '0' in bit position 1, register
offset 4
Disables the transmitter function and
enables the receiver function
The RS-485 port is configured for termination for either marking or
spacing idle condition, or not terminated. Any node located between the
end points should not be terminated. Use W1[1-2][3-4] to disable termi-
nation. Jumper W1[7-9][8-10] to provide for marking condition and
make sure that both ends of the network are terminated.
Table 5-15 RS-485 termination select jumper: W1
Pins Description
[7-8]* RS-485 terminated(-), idle line at mark
[9-10]* RS-485 term), idle line at mark
[7-9] RS-485 terminated(-), idle line at space
[8-10] RS-485 term), idle line at space
* = default
Note: For no termination, remove jumpers from pins 7, 8, 9, and 10.
Table 5-16 RS-485 and TTL interfaces
For RS-485 interface For TTL interface
Pin 1 RS-485+ Pin 1 TTL RD
Pin 2 TxD Pin 2 TxD
Pin 3 Gnd Pin 3 Gnd
Pin 4 RS-485– Pin 4 NA
W1[1-2][3-5][4-6]* W1[2-4][5-6]
* = default
≡
RS-485 network
An application may implement a node as either the “host” node or as a
“remote” node in an RS-485 network. There can be as many as 32 nodes
without any bus repeaters in the network. A “host” is referred to as the
node that initiates communication; while a “remote” is referred to as a
node that is addressed by the host.
In any given communication sequence in an RS-485 network, there can
only be one host. The host is responsible for initiating communication,
maintaining network registration, and providing housekeeping tasks
with other nodes. Remotes, however, cannot initiate a communication.