Intel 8XC196MH, 8XC196MD, 8XC196MC manual 12.3 A/D Converter Operation, P1PIN MC,MD

		ANALOG-TO-DIGITAL (A/D) CONVERTER
	Table 12-2. A/D Control and Status Registers (Continued)
Mnemonic	Address	Description
P0_PIN	1FA8H (MC, MD)	Port 0 Pin State
	1FDAH (MH)	Read P0_PIN to determine the current values of the port 0 pins.
		Reading the port induces noise into the A/D converter, decreasing
		the accuracy of any conversion in progress. We strongly
		recommend that you not read the port while an A/D conversion is in
		progress. To reduce noise, the P0_PIN register is clocked only
		when the port is read.
P1_PIN (MC,MD)	1FA9H (MC, MD)	Port 1 Pin State
		Read P1_PIN to determine the current values of the port 1 pins.
		Reading the port induces noise into the A/D converter, decreasing
		the accuracy of any conversion in progress. We strongly
		recommend that you not read the port while an A/D conversion is in
		progress. To reduce noise, the P1_PIN register is clocked only
		when the port is read.

12.3 A/D CONVERTER OPERATION

An A/D conversion converts an analog input voltage to a digital value, stores the result in the AD_RESULT register, and sets the A/D interrupt pending bit. An 8-bit conversion provides

20mV resolution, while a 10-bit conversion provides 5 mV resolution. An 8-bit conversion takes less time than a 10-bit conversion because it has two fewer bits to resolve and the comparator re- quires less settling time for 20 mV resolution than for 5 mV resolution.

You can convert either the voltage on an analog input channel or a test voltage. Converting the test inputs allows you to calculate the zero-offset error, and the zero-offset adjustment allows you to compensate for it. This feature can reduce or eliminate off-chip compensation hardware. Typ- ically, you would convert the test voltages and adjust for the zero-offset error before performing conversions on an input channel. The AD_TEST register allows you to program a zero-offset ad- justment.

A threshold-detection compares an input voltage to a programmed reference voltage and sets the A/D interrupt pending bit when the input voltage crosses over or under the reference voltage.

A conversion can be started by a write to the AD_COMMAND register or it can be initiated by the EPA, which can provide equally spaced samples or synchronization with external events. (See“Programming the EPA and Timer/Counters” on page 11-15.) The A/D scan mode of the pe- ripheral transaction server (PTS) allows you to perform multiple conversions and store their re- sults. (See “A/D Scan Mode” on page 5-32.)

12-3