PCE84C486 datasheet(18/36 Pages) PHILIPS

18 / 36 page

1996 Feb 21

Philips Semiconductors

Objective speciﬁcation

Microcontrollers for digital auto-sync and

VST TV controller applications

PCE84C486; PCE84C487

7. For the DAC = 1100 case

If COMP = 1; then the analog input voltage is still

greater than Vref and therefore the digital input to the

DAC needs to be increased again. Set the input to the

DAC to 1110.

If COMP = 0; then the analog input voltage is now less

than Vref and therefore the digital input to the DAC

needs to be decreased. Set the input to the DAC to

1010

8. For the DAC = 0100 case

If COMP = 1; then the analog input voltage is now

greater than Vref 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 Vref 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 6, 7 and 8 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.16.

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 (VA) is determined

using Equation (4):

(4)

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

change the value of Vref; select the ADC channel and read

the COMP bit.

----------

DAC value

()

Fig.15 Block diagram of 2 channel ADC.

handbook, full pagewidth

4-BIT DAC

COMPARATOR

DAC3

DAC2

DAC1

DAC0

ADCE1

ADCE2

ADCS1

ADCS0

MGD263

ADC enable selection

DAC value selection

ENABLE

SELECTOR

ADC

CHANNEL

SELECTOR

DP12/ADC2

DP11/ADC1

Vref

DERIVATIVE PORT

SELECTOR

EN1

EN2

‘MOV A, D20’

instruction

to read COMP bit

COMP bit

Internal bus

Channel selection

−

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