Datasheet

Analog-to-Digital Converter (ADC)
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
44 Freescale Semiconductor
AIEN — ADC Interrupt Enable Bit
When this bit is set, an interrupt is generated at the end of an ADC conversion. The interrupt signal is
cleared when the ADR register is read or the ADSCR register is written. Reset clears the AIEN bit.
1 = ADC interrupt enabled
0 = ADC interrupt disabled
ADCO — ADC Continuous Conversion Bit
When set, the ADC will convert samples continuously and update the ADR register at the end of each
conversion. Only one conversion is allowed when this bit is cleared. Reset clears the ADCO bit.
1 = Continuous ADC conversion
0 = One ADC conversion
ADCH4–ADCH0 — ADC Channel Select Bits
ADCH4–ADCH0 form a 5-bit field which is used to select the input for the A/D measurement.
The choices are one of four ADC channels, as well as V
REFH
and V
SS
. Input selection is detailed in
Table 3-1. Care should be taken when using a port pin as both an analog and a digital input
simultaneously to prevent switching noise from corrupting the analog signal.
The ADC subsystem is turned off when the channel select bits are all set to 1. This feature allows for
reduced power consumption for the MCU when the ADC is not used. Reset sets these bits.
NOTE
Recovery from the disabled state requires one conversion cycle to stabilize.
Table 3-1. Mux Channel Select
ADCH4 ADCH3 ADCH2 ADCH1 ADCH0 Input Select
0 0 0 0 0 PTB0
0 0 0 0 1 PTB1
0 0 0 1 0 PTB2
0 0 0 1 1 PTB3
00100
Unused
(1)
1. If any unused channels are selected, the resulting ADC conversion will be unknown.
—————
—
11100
Unused
(1)
11101
V
REFH
(2)
2. The voltage levels supplied from internal reference nodes as specified in the table are used
to verify the operation of the ADC converter both in production test and for user applica-
tions.
11110
V
SSAD
(2)
1 1 1 1 1 ADC power off