Dwyer MPC User Manual
Page 15
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OPTION 232, 485 SERIAL COMMUNICATION OPERATION
The serial communications options allow the control to be written to and read from a
remote computer or other similar digital device. Communication is allowed either through a
RS-485 (Option 485) port, or a RS-232 (Option 232) port.
Wire the communication lines as shown on Page 7. Wiring for the RS-485 is run from
control to control in a daisy chain fashion with a termination resistor (120 ohms) across the
transmit and receive terminals of the last control in the chain. Set the RS-485 DIP switch
for half or full duplex as appropriate for your application. The DIP switch is located on the
communications board plugged into the center of the bottom board of the control.
Select the control address and communication baud rate with the
Addr
and
bAUd
menu
items in the Secure Menu. THE BAUD RATE AND ADDRESS MENU ITEMS WILL TAKE
EFFECT ON THE NEXT POWER UP OF THE CONTROL. BE SURE TO POWER CYCLE
THE CONTROL BEFORE USING THE NEW BAUD RATE AND ADDRESS.
In operation, you have the option of preventing a write command from the host computer.
To prevent the host from writing to the control change the
L0rE
menu item in the
Secondary Menu to
L0C
. To allow the host to write commands to the control set
L0rE
to
rE
.
(The host does have the ability to change the
L0rE
state, but it is not automatic.)
If your system depends on constant reading or writing to and from the host, you may wish
to set the No Activity Timer (
nAt
) to monitor the addressing of the control. When the
L0rE
is set to
rE
and the
nAt
is set to any value other than
0FF
, the control will expect to be
addressed on a regular basis. If the control is not addressed in the time set by the value of
nAt
, then the control will display the error message
CHEC LorE
. To clear the message set
L0rE
to
L0C
.
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