Analog Output; Figure 7: Schematic Diagram Of The A/D Converter; Figure 8: Schematic Diagram Of D/A Converters - OEM BL2500 User Manual

PLC BL2500 User's Manual
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The A/D converter programs DA0 using a successive-approximation binary search until DA0 equals the
A/D converter input voltage. That programmed DA0 voltage is then reported as the A/D converter value.
The A/D converter transforms the voltage at DA0 into a 13.2 mV window around DA0. Because the A/D
converter circuit uses a 13.2 mV window, the accuracy is ±6.6 mV. DA0 can range from 0.1 V to 3.1 V,
which represents 227 steps of 13.2 mV. This represents a resolution of approximately 8 bits. Since the
D/A converter is able to change the DA0 output in 3.22 mV steps, there are 930 steps over the range
from 0.1 V to 3.1 V. This represents a resolution of approximately 10 bits.
The A/D converter has no reference voltage. There is a relative accuracy between measurements, but no
absolute accuracy without calibration. This is because the +3.3 V supply can vary ±5%, the pulse-width
modulated outputs might not reach the full 0 V and 3.3 V rails out of the Rabbit 3000 microprocessor, and
the gain resistors used in the circuit have a 1% tolerance. For these reasons, each BL2500 needs to be
calibrated individually, with the constants held in software, to be able to rely on an absolute accuracy. The
BL2500 has this calibration support.
An A/D conversion takes approximately 83 ms.

4.4 ANALOG OUTPUT

Two D/A converter outputs, DA0 and DA1, are supplied on the BL2500. These are shown in Figure 8.
Note:
Only DA1 is available for
The D/A converters have no reference voltage. Although they may be fairly accurate from one
programmed voltage to the next, they do not have absolute accuracy. This is because the +3.3 V supply
can change ±5%, the PWM outputs might not achieve the full 0 V and 3.3 V rail out of the processor, and
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Figure 7: Schematic Diagram of the A/D Converter

PLC BL2500 as DA0 is used by the A/D converter.
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Figure 8: Schematic Diagram of D/A Converters

Hardware Reference
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