Intel 8XC196MH, 8XC196MD Determining A/D Status and Conversion Results, Adresult Read, ADRLT90

ANALOG-TO-DIGITAL (A/D) CONVERTER

12.5 DETERMINING A/D STATUS AND CONVERSION RESULTS

You can read the AD_RESULT register (Figure 12-6) to determine the status of the A/D convert- er. The AD_RESULT register is cleared when a new conversion is started; therefore, to prevent losing data, you must read both bytes before a new conversion starts. If you read AD_RESULT before the conversion is complete, the result is not guaranteed to be accurate.

The conversion result is the ratio of the input voltage to the reference voltage:

VIN – ANGND	VIN – ANGND
RESULT (8-bit)= 255 × ------------------------------------------	RESULT (10-bit)= 1023 × ------------------------------------------
VREF – ANGND	VREF – ANGND

You can also read the interrupt pending register (see Table 12-2 on page 12-2) to determine the status of the A/D interrupt.

AD_RESULT (Read)	Address:	1FAAH
	Reset State (MC, MD):	FFC0H
	Reset State (MH):	7FC0H

The A/D result (AD_RESULT) register consists of two bytes. The high byte contains the eight most- significant bits from the A/D converter. The low byte contains the two least-significant bits from a ten- bit A/D conversion, indicates the A/D channel number that was used for the conversion, and indicates whether a conversion is currently in progress.

15

ADRLT9 ADRLT8 ADRLT7 ADRLT6

7

ADRLT1 ADRLT0 — STATUS

8

ADRLT5 ADRLT4 ADRLT3 ADRLT2

0

ACH3 ACH2 ACH1 ACH0

Bit	Bit	Function
Number	Mnemonic
15:6	ADRLT9:0	A/D Result
		These bits contain the A/D conversion result.
5	—	Reserved. This bit is undefined.
4	STATUS	A/D Status
		Indicates the status of the A/D converter. Up to 8 state times are required
		to set this bit following a start command. When testing this bit, wait at
		least the 8 state times.
		0 = A/D is idle
		1 = A/D conversion is in progress
3:0	ACH3:0	A/D Channel Number
		These bits indicate the A/D channel number that was used for the
		conversion.
	Figure 12-6. A/D Result (AD_RESULT) Register — Read Format
		12-9