Explanation on Example 6

Example 6 Function	This Example 6 program reads the analogue input voltage at the ADC input and displays it on the scope via the DAC.
Step u	The processor triggers the ADC to conduct an A-to-D conversion every 50 us. To trigger, the processor creates a positive edge on the signal WR. To maintain the 50 us period, the processor utilizes Timer 0 to constitute a 50-us timer.
Step v	When the ADC completes an A-to-D conversion, it creates a negative edge on the signal INTR. This signal serves as an external interrupt to the processor.
Step w	After the processor receives the external interrupt from the ADC, it puts the RD pin of the ADC at the low level. The low level on the RD signal enables the output D7~D0 of the ADC. The processor reads the ADC output at Port 2 and then moves it to Port 1, for the input of the DAC.
	Note: The ADC can convert an analog voltage into a binary number in 25 us.

Actions in Example 6:

This program reads the analogue input voltage on the ADC and displays it on the scope via the DAC.

A sample is taken from the ADC every 50 us.

This is achieved by setting timer 0 to interrupt the main program every 50 us.
The timer 0 ISR then initiates an ADC conversion.

When the conversion is complete the ADC interrupt line goes low.

This line is interfaced with the 8051 external 0 interrupt line.

The external 0 ISR therefore takes the reading from the ADC on P2 and passes it to the DAC on P1.

Therefore, while the program is running, the scope voltage level should be the same as the ADC input voltage.
However, when a change is made to the ADC input voltage it will take some time for the scope to update.

(ie: until the next timer 0 interrupt).

Note: when running this program make sure the ADC is enabled (not the comparator).

ADC enabled; comparator disabled. Comparator enabled; ADC disabled.

ADC Pin Function

Name	Direction	Value	Function
WR	Input	Positive edge	Initialize an Analog-to-Digital conversion
		Otherwise	No effect.
INTR	Output	Positive edge	Issue an interrupt to inform the processor that a conversion has been finished.
		Otherwise	No effect.
PD	Input	PD = 0	Enable the output D7~D0 The data pins become lo-Z. The data can be read by the processor
		PD = 1	Disable the output D7~D0. The data pins become hi-Z. The data cannot be read by the processor.