Chapter 4 Theory of Operation
© National Instruments Corporation 4-5 DAQCard-1200 User Manual
Each 82C53 contains three independent 16-bit counter/timers and one 8-bit
Mode Register. Each counter has a CLK input pin, a GATE input pin, and
an OUT output pin. You can program all three counter/timers to operate in
several useful timing modes.
The first group of counter/timers is called Group A and includes A0, A1,
and A2. You can use these three counters for internal data acquisition and
DAC timing, or you can instead use the three external timing signals,
EXTCONV*, EXTTRIG and EXTUPDATE*, for data acquisition and
DAC timing.
The second group of counter/timers is called Group B and includes B0, B1,
and B2. You can use counters B0 and B1 for internal data acquisition and
DAC timing, or you can use the external timing signal CLKB1 for analog
input timing. If you are not using Counters B0 and B1 for internal timing,
you can use these counters as general purpose counter/timers. CounterB2
is reserved for external use as a general purpose counter/timer.
For a more detailed description of Counter Group A and Counters B0
andB1, refer to the following Analog Input and Analog Output sections.
Analog InputThe DAQCard-1200 has eight channels of analog input with
software-programmable gain and 12-bit A/D conversion. The
DAQCard-1200 also contains data acquisition timing circuitry for
automatic timing of multiple A/D conversions and includes advanced
options such as external triggering, gating, and clocking. Figure4-4 shows
a block diagram of the analog input circuitry.