Registers
Control of the ADC is provided in the ADC control register located at index 12h. This register is defined as follows:
Bit Value Mode Description
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[0] 0 R/W ADCE ADC enable; 1=enabled; should be disabled when not
in use to save power.
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[1:2] 00 R/W CNS[0:1] Channel select bits.
00 = ADC[0], system batteries
01 = ADC[1], backup battery
10 = ADC[2], reference voltage
11 = VSS
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[3] - R TOHI Comparator output; high when DAC output value is
above analog input
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[4] - R BSY Busy bit; a/d convertor is in the middle of a
conversion.
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[5:7] - - unused
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The value input to the DAC is written to the DAC value register located at 13h. This is a 6-bit value, the 2 MSBs are unused. Writing the value register causes a comparison to occur. This comparison will take up to 62uS.