Analog Output; Digital I/O; Power Distribution; Input Impedance Configuration - Measurement Computing PCI-DAS4020/12 User Manual

PCI-DAS4020/12 User's Guide

Analog output

Two 12-bit voltage outputs are software programmable for ±10 V or ±5 V. The D/A is the Analog
Devices AD7237 Dual DAC. Since the DAC is dual buffered, the DAC output voltage is updated after
the MS nibble is written to the DAC.
The DACs initially power-up and are reset to 0 V. There is no calibration on these DACs. The offset and
gain errors are minimized by using precision components.
DAC Range Input Code Binary
± 10 V 0000 0000 0000
± 10 V 1000 0000 0000
± 10 V 1111 1111 1111
± 5 V 0000 0000 0000
± 5 V 1000 0000 0000
± 5 V 1111 1111 1111

Digital I/O

The digital I/O is an 82C55 digital logic device. An external interrupt source pin (pin 1) and external
interrupt enable pin (pin 3) on the auxiliary 40-pin connector (
lines are pulled up and an OR operation is performed on them to generate the external interrupt signal.
Both are active low.

Power distribution

The PCI-DAS4020/12 board is powered by the PCI bus. The only power used is +5 V.

Input impedance configuration

Each analog input and the trigger/clock input channel on the PCI-DAS4020/12 has a dedicated solder
gap. A solder gap consists of two copper pads that you can solder together to change the input impedance
of the channel. When the solder gaps are open (default), the input impedance is 1.5 Mohm. When the
solder gaps are closed, the input impedance is 50 ohm.
To close the solder gaps and change the impedance to 50 ohm, solder the two copper pads together. To
close the solder gap, touch a soldering iron to the two contacts until some rosin core solder flows across
the copper pads and forms a small blob of solder. Be careful not to overheat the pads, or they may
delaminate from the circuit board. Do not add too much solder, as it could flow onto other components
and cause an electrical short or other defect.
Table 4-2. DAC input coding
12 bit Input Code Hex
000h
800h
FFFh
000h
800h
FFFh
Figure 4-2. Analog output block diagram
4-2
Table 4-2 shows the DAC input coding.
12 bit Output Voltage
−10.000 V
0 V
+9.99513 V
−5.000 V
0 V
+4.99756 V
) are used for external interrupts. These
P3
Functional Details