Real Time Devices AD1200 User Manual page 34

The 1200 board has four major circuits, the A/D, the D/A (ADA1200 only), the timer/counters, and rhe digitat
I/O lines. Figure 3-1 shows the block diagtam of ttre board. This chapter describes the hardware which makes up the
major circuits and hardware-selectable intemrpts.
A/D Conversion Circuitry
The1200 performs analog-to-digital conversions on up to 16 single-ended software-selectable analog input
channels. The following paragraphs describe ttre A/D circuitry.
Analog Inputs
The input voltage range is jumper-selectable for -5 to +5 volts, -10 to +10 volts, or 0 to +10 volts. Resistor
configurable gain lets you amplify lower level signals to more closely match the board's input ranges. This gain
circiutry is described in Chapter 1. Overvoltage protection to +35 volts is provided at the inputs.
A/D Converter
The AD678 12-bit successive approximation A/D convert€r accurately digitizes dynamic input voltages in
5 microseconds, for a maximum throughput rate of 200 kHz for the converter alone. The AD678 contains a sample-
and-hold amplifier, a 72-bit A/D converter, a 5-volt reference, a clock, and a digitat interface to provide a complete
A/D conversion function on a single chip. Irs low-power CMOS logic combined with a high-precision, low-noise
design give you accurate results.
Conversions are initiated through software (internally riggered) or by using an extemal trigger brought onto the
board through the I/O conneclor. An on-board pacer clock can be used to control the conversion rate. Conversion
modes are described in Chapter 4, Board Operation and Programming.
Fig. 3-1 - AD1200/ADA1 200 Block Diagram
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