Issue
Selecting the correct terminating resistor for RS485 serial daisy chain.
Product Line
Powerlogic and ION Meters, Other RS485 devices
Environment
Applications using a serial RS485 daisy chain
Cause
Need to terminate the end of serial RS-485 device chain.
Resolution
MCT485 is spade connector whereas MCTAS485 and MCT2W have straight lead. Although, the resistance and capacitance is the same in each part. More details for individual terminators are shown below:
MCT485- Network Terminator Circuit Monitor, Part Number: 3090MCT485 (as shown in Screenshot A)
- 1 100 ohm, .25W resistor in series with 1 .047uF capacitor used across RX+ to RX-
- 1 100 ohm, .25W resistor in series with 1 .047uF capacitor used across TX+ to TX-
MCTAS485 -Network Terminator PowerLogic Compatible, Part Number: 3090MCTAS485 (as shown in Screenshot B)
- 1 100 ohm, .25W resistor in series with 1 .047uF capacitor used across RX+ to RX-
- 1 100 ohm, .25W resistor in series with 1 .047uF capacitor used across TX+ to TX-
MCT2W- RS485 Terminator for 2-Wire Daisy Chain, Part Number: MCT2W (as shown in Screenshot C)
- Old Version: 1 100 ohm, .25W resistor in series with 1 .047uF capacitor used across + to -
- New Version: 1 100 ohm resistor used across + to -
Screenshot A (3090MCT485)
Screenshot B (3090MCTAS485 )
Screenshot C (MCT2W)
NOTE: See attached document for internal wiring diagram of the MCTAS485. The wiring diagram is the same for the MCT485
