Nominal
Max
Notes
Line load currents
RS-232 line load
2 mA
per load
–
Average expected increase in drawn
current per RS-232 line connected in
idle or active modes (no extra current
in standby mode).
Both TX and RTS are considered to be
RS-232 loads.
RS-485 line load
2
40 mA
3
77 mA
4
This extra current is only present when
actively transmitting
1
All currents are measured with no loads connected.
2
The RS-485 transmit pair is disabled when not transmitting in order to save power. Higher value resistors can be
used to save power dependent upon the application. For many applications, especially with shorter cable runs, no
load/termination resistors will be needed.
3
Single 100 Ω load between transmit lines. Two 100 Ω resistors (one on each end) is the maximum recommended
loading. Removing any termination resistance should dramatically decrease current consumption during transfer
of data.
4
The RS-485 interface is protected against short circuits via a 44 Ω resistance making this the maximum current
possible even during short circuit. This resistance is part of the ESD protection circuitry and will be present at all
times; it shouldn’t affect normal circuit operations.
(p. 37) shows the circuit in detail.
5.2.2 Voltage specifications
Connection
Minimum
voltage
1
Nominal
voltage
1
Maximum
voltage
1
Power supply, +12 V connection
2
9 V
12 V
30 V
RS-232 input threshold low
0.8 V
–
–
RS-232 input threshold high
–
–
2.4 V
RS-232 input absolute maximum
2
–
±15 V
±18 V
RS-232 input resistance
3 kΩ
5 kΩ
7 kΩ
RS-232 output voltage swing
3
±5 V
±5.4 V
–
RS-485 input (differential)
200 mV
4
–
6 V
RS-485 output (differential)
1.5 V (at 50 Ohms)
–
–
SDM-SIO2R Serial Input/Output Module with Switched Sensor Power
6
