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Chapter 4 Theory of Operation
© National Instruments Corporation 4-5 PCI-1200 User Manual
timing, or you can use the three external timing signals, EXTCONV*,
EXTTRIG, and EXTUPDATE*, for DAQ 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 DAQ 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. Counter B2 is
reserved for external use as a general purpose counter/timer.
For a more detailed description of counter group A and
counters B0 and B1, refer to the Analog Input and Analog Output sections.
Analog Input
The PCI-1200 has eight channels of analog input with
software-programmable gain and 12-bit A/D conversion. The PCI-1200
also contains DAQ timing circuitry for automatic timing of multiple A/D
conversions and includes advanced options such as external triggering,
gating, and clocking. Figure 4-4 shows a block diagram of the analog input
circuitry.
Figure 4-4.
Analog Input Circuitry
Sample-
and-Hold
Amp
DAQ
Timing
Gain Select/
Mux Counter
+
Program-
mable
Gain Amp
–
ADC
A/D
FIFO
External Trigger
Counter/Timer
Signals
WRT/RD
CONV
AVAIL
A/D
RD
EXTCONV*
OUTB1
EXTTRIG
ACH0
ACH1
ACH2
ACH3
ACH4
ACH5
ACH6
ACH7
12
12
8
6
A/D
Data
Data
Data
GAIN0
GAIN1
GAIN2
Convert
Mux
ACH1
ACH3
ACH5
ACH7
AISENSE/
AIGND
External Convert
External Scan Interval
Dither
Circuitry
Dither Enable
Dither
PCI Bus
Digital
Control
Logic
MITE
PCI
Interface
Chip
Data/Address
Interface Control
Error Reporting
Arbitration
System
Interrupt
1
2
2
2
6
37
Address
Data
Control
Interrupt
1
DRQ
1
4
8
5
I/O Connector
Mux