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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
2
SDM-SIO1A and SDM-SIO4A Serial Input/Output Modules
Nominal
Max
General currents
110 µA
400 µA
500 µA
1200 µA
4.8 mA
6 mA
3.2 mA
4.5 mA
9.6 mA
12 mA
11.7 mA
13 mA
Line load currents
2 mA per
–
load
40 mA
77 mA
3
All currents are measured with no loads connected. For the SDM-SIO4A, the currents
1
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.
Single 100 Ω load between transmit lines. Two 100 Ω resistors (one on each end) is
3
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. FIGURE 7-1, RS-485 Internal Circuit Diagram
circuit in detail.
5
Maximum current is only at maximum operational temperatures.
Notes
Current after SerialClose()
(5)
has been called
1
After SerialOpen() has been called
After SerialOpen() in receive-only
mode
Active RS-232 command
Active RS-485 command (no
termination resistors)
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.
This extra current is only present when
4
actively transmitting
, shows the
(p. 25)
5
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