User Guide
3
discarded until space is made when the logger requests data from the
SDM-SIO1.
2.2 Electrical parameters
2.2.1 SDM-SIO1 current consumption
Nominal
Max
Notes
General currents
Standby current
70 uA
100 uA
Current after SerialClose has been called.
RS-232 and RS-485 current consumption
(1)
Idle current
5.5 mA
6 mA
After SerialOpen has been called
Idle current (receive only)
4.1 mA
4.5 mA
After SerialOpen in receive only mode
Active current (RS-232)
11. 5mA
12 mA
Active RS-232 command
Active current (RS-485)
12.5 mA
1 3mA
Active RS-485 command (no termination
resistors)
Line load currents
RS-232 line load
2 mA per
load
3 mA per
load
Average expected increase in drawn
current per RS-232 line connected in idle
or active modes (no extra current in
stand-by 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 100R load between transmit lines. Two 100R 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 44R 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. The ‘RS-485 internal circuit diagram’ on p.10 of this manual shows the circuit
in detail.
