DA-660A Series HW UM
Hardware Connection Description
3-4
Configurable Pull High/Low Resistors for the RS-485 Port
In some critical environments, you may need to add termination resistors to prevent the reflection of serial
signals. When using termination resistors, it is important to set the pull high/low resistors correctly so that
the electrical signal is not corrupted. The DA-660A uses jumper settings to set the termination resistors and
pull high/low resistor values for each serial port.
To configure the termination and pull high/low resistors for the serial connections, you first need to open the
chassis if the computer. You will see 3 rows of jumper caps (as shown in the accompanying figure). The first
row is for setting pull high resistors, the second row is for setting termination resistors, and the third row is
for setting pull low resistors.
Each serial port has 6 jumper caps for configuring the resistors. The pin assignments are shown in the
following table:
Jumper setting
RS485 Data +
RS485 Data -
Pull High resistors
1-2: 150
kΩ
2-3: 1
kΩ
Termination
1-2: Open
2-3: 120
Ω
Pull Low resistors
1-2: 150
kΩ
2-3: 1
kΩ
To set the termination resistors to 120 Ω, make sure that PIN 2 and PIN 3 assigned to the serial port are
shorted by jumper caps.
To set the pull high/low resistors to 150 k
Ω, make sure that PIN 1 and PIN 2 assigned to the serial port are
shorted by jumper caps. This is the default setting.
To set the pull high/low resistors to 1 k
Ω, make sure that PIN 2 and PIN 3 assigned to the ser
ial port are
shorted by jumper caps.
