P83CX80 Datasheet, PDF (37/84 Pages) NXP Semiconductors – 80C51 type core

Philips Semiconductors
Microcontrollers for monitors with DDC
interface, auto-sync detection and sync proc.
Product specification
P83Cx80; P87C380
8. For the DAC = 0100 case.
If COMP = 1; then the analog input voltage is now
greater than V_ref and therefore the digital input to the
DAC needs to be increased. Set the input to the DAC
to 0110.
If COMP = 0; then the analog input voltage is still lower
than V_ref and therefore the digital input to the DAC
needs to be decreased again. Set the input to the DAC
to 0010.
9. The operations detailed in 5, 6 and 7 above are
repeated and each time the digital input to the DAC is
changed accordingly; as dictated by the state of the
COMP bit.
The complete process is shown in Fig.21. Each time
the DAC input is changed the number of values which
the analog input can take is reduced by half. In this
manner the actual analog value is honed into. The
value of the analog input (V_A) is determined by the
formulae:
V_A = -V--1--^D-6--^D-- × (DAC value + 1)
As the conversion time of each compare operation is
greater than 6 µs but less than 9 µs; a NOP instruction is
recommended to be used in between the instructions that
select V_ref; the ADC channel and read the COMP bit.
handbook, full pagewidth
P3.3/ADC1
P3.2/ADC0
ADC
CHANNEL
SELECTOR
PORT INTERFACE
EN0
EN1
+
Vref
−
COMPARATOR
EN
internal bus
COMP bit
MOV A, ADCDAT
instruction
to read COMP bit
channel selection DACHL
ENABLE
SELECTOR
4-BIT DAC
ADCE
ADC enable selection
DAC3 DAC2 DAC1 DAC0
DAC value selection
MGG049
Fig.20 Block diagram of the ADC.
1997 Dec 12
37