PC expansion bus systems - PC Based Instrumentation and Control - page 103

Photo 2.16 Arcom's APCI-ADADIO multifunction I/O card (photo courtesy
of Arcom)

5 Write any value to Base + 1 in order to initiate conversion

6 Wait for approximately 20 µ s for the conversion to complete

7 Read Base + 1 and check that bit 0 is at logic 0 (i.e. conversion completed)

8 Read Base + 2 ADC data low nibble (bits 0 to 3)

9 Read Base + 3 ADC data high byte (bits 4 to 11).

The APCI-ADADIO contains two 12-bit digital-to-analogue converters.
On-board links can be used to select between three possible output voltage
ranges, 5 V, 0-5 V, and 0-10 V. the DAC values are updated by writing to the
data register at Base+2 (low nibble bits 0 to 3) and Base + 3 (high byte bits 4 to
11). Prior to this the DAC channel must be selected by writing a value of 02H
to the index register for DAC A and 03H for DAC B.
The APC-ADADIO provides 16 digital I/O lines grouped in four nibbles.
Each nibble has a power-up/reset state link and can be programmed as either
input or output via the digital I/O configuration register. Access to individ-
ual I/O lines are made possible via index registers 0AH and 0BH. Reading
these provide the status of all I/O lines regardless of whether they are config-
ured as input or output. With some careful programming it is also possible
to use these lines in bi-directional mode. Note that, if a nibble is to be
used as an input the corresponding reset state link must be set to the high
position otherwise the lines will be driven low as outputs which may cause
damage.
The APCI-ADADIO uses an 8254 compatible counter/timer. This provides
three individual 16-bit counter/timers. Channel 0 can be used to trigger an
analogue-to-digital conversion (as mentioned earlier) whilst Channel 1 may be
used to generate an interrupt request sequence.