Dwyer MPCJR - Manual (Page 14)

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 L O r E menu
item in the Secondary Menu to LOC. To allow the host to write commands to the
control set LOrE to rE. (The host does have the ability to change the LOrE 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 LOrE is set to rE and the nAt is set to any value other than OFF, 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 LOrE t o LOC.
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