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5.2 Electrical parameters
5.2.1 Current consumption
Standby current SDM-SIO1A
Standby current SDM-SIO4A
RS-232 and RS-485 current consumption (per active port)
Idle current
Idle current (receive only)
Active current (RS-232)
Active current (RS-485)
RS-232 line load
RS-485 line load
1
All currents are measured with no loads connected. For the SDM-SIO4A, the currents quoted need to be totalized
to allow for the state of each active serial port.
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.
Nominal
General currents
110 µA
500 µA
4.8 mA
3.2 mA
9.6 mA
11.7 mA
Line load currents
2 mA
per load
2
3
40 mA
Figure 7-1
SDM-SIO1A and SDM-SIO4A Serial Input/Output Modules
Max
150 µA
Current after
850 µA
After
6 mA
After
4.5 mA
in receive-only mode
12 mA
Active RS-232 command
Active RS-485 command (no
13 mA
termination resistors)
Average expected increase in drawn
current per RS-232 line connected in
idle or active modes (no extra current
–
Both TX and RTS are considered to be
This extra current is only present
4
77 mA
when actively transmitting
(p. 27) shows the circuit in detail.
Notes
SerialClose()
has been called
1
SerialOpen()
has been called
SerialOpen()
in standby mode).
RS-232 loads.
5
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