MC68HC908MR8 Datasheet, PDF (316/372 Pages) Motorola, Inc – Microcontrollers

Analog-to-Digital Converter (ADC)
is used when compatibility with 8-bit ADC designs are required. No
interlocking between ADRH and ADRL is present.
NOTE: Quantization error is affected when only the most significant eight bits
are used as a result. See Figure 18-2.
8-BIT 10-BIT
RESULT RESULT
003
00B
IDEAL8-BIT CHARACTERISTIC
WITH QUANTIZATION = ±1/2
10-BIT TRUNCATED
TO 8-BIT RESULT
00A
IDEAL 10-BIT CHARACTERISTIC
009 WITH QUANTIZATION = ±1/2
002 008
007
006
005
001 004
003
WHEN TRUNCATION IS USED,
ERROR FROM IDEAL 8 BIT = 3/8 LSB
002
DUE TO NON-IDEAL QUANTIZATION.
001
000 000
1/2
2 1/2
4 1/2
6 1/2
8 1/2
INPUT VOLTAGE
1 1/2
3 1/2
5 1/2
7 1/2
9 1/2
REPRESENTED AS 10-BIT
INPUT VOLTAGE
1/2
1 1/2
2 1/2
REPRESENTED AS 8-BIT
Figure 18-2. 8-Bit Truncation Mode Error
18.4.6 Monotonicity
The conversion process is monotonic and has no missing codes.
18.5 Interrupts
When the AIEN bit is set, the ADC module is capable of generating a
CPU interrupt after each ADC conversion. A CPU interrupt is generated
if the COCO bit is at logic 0. The COCO bit is not used as a conversion
complete flag when interrupts are enabled.
Technical Data
316
Analog-to-Digital Converter (ADC)
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor