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M2i.30xx / M2i.30xx-exp Manual
Introduction
Option Digital Differential Inputs
Option Digital Differential Inputs
Introduction
The special option „Digital Differential Inputs“ allows the use of two adjacent single ended channels in a true differential mode. Both channels
are sampled parallelly single-ended with their dedicated ADCs and afterwards the subtraction is made in the digital domain. The inputs are
still related to GND and may not have a common voltage level exceeding the respective single-ended input range.
As all of the available SE input ranges remain the same spoken in absolute voltage levels when using the digital differential mode, the resulting
input range in terms of differential inputs doubles. The drawing shows this as an example for an single-ended input range of ±10 V:
Sample format
The 12 bit A/D samples are stored in twos complement in the16 bit data word with a sign-extension. The overrange mode is not available
when the digital differential feature is installed on the card.
Single-ended modes
12 bit resolution means that data is ranging from -2048…to…+2047. In standard mode the upper four bits contain the sign extension allow-
ing to directly use the read data as 16 bit integer values. If digital inputs are activated these digital inputs are stored in the four upper bits of
the 16 bit data word.
Digital differential mode
The digital differential mode samples the input with two 12 bit converters (each one for the true and the complementary input phase) and
does the subtraction in the digital domain. Therefore the result is a 13 bit digital twos complement value means that data is ranging from
-4096…to…+4095. This value is stored in a 16 bit data word with sign extension. The digital input option cannot be activated together with
the digital differential mode.
Bit
Single-ended
Standard Mode
Single-ended
Digital inputs (option)
enabled
Digital Differential
Standard Mode
D15
ADx Bit 11 (MSB)
Digital bit 3 of channel x
ADx Bit 12 (MSB)
D14
ADx Bit 11 (MSB)
Digital bit 2 of channel x
ADx Bit 12 (MSB)
D13
ADx Bit 11 (MSB)
Digital bit 1 of channel x
ADx Bit 12 (MSB)
D12
ADx Bit 11 (MSB)
Digital bit 0 of channel x
ADx Bit 12 (MSB)
D11
ADx Bit 11 (MSB)
ADx Bit 11 (MSB)
ADx Bit 11
D10
ADx Bit 10
ADx Bit 10
ADx Bit 10
D9
ADx Bit 9
ADx Bit 9
ADx Bit 9
D8
ADx Bit 8
ADx Bit 8
ADx Bit 8
D7
ADx Bit 7
ADx Bit 7
ADx Bit 7
D6
ADx Bit 6
ADx Bit 6
ADx Bit 6
D5
ADx Bit 5
ADx Bit 5
ADx Bit 5
D4
ADx Bit 4
ADx Bit 4
ADx Bit 4
D3
ADx Bit 3
ADx Bit 3
ADx Bit 3
D2
ADx Bit 2
ADx Bit 2
ADx Bit 2
D1
ADx Bit 1
ADx Bit 1
ADx Bit 1
D0
ADx Bit 0 (LSB)
ADx Bit 0 (LSB)
ADx Bit 0 (LSB)
