mc68hc908gr8vp Freescale Semiconductor, Inc, mc68hc908gr8vp Datasheet - Page 56

• Manufacturer Part Number: mc68hc908gr8vp
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Analog-to-Digital Converter (ADC)
5.3.2 Voltage Conversion
When the input voltage to the ADC equals V
input voltage equals V
straight-line linear conversion. All other input voltages will result in $FF, if greater than V
5.3.3 Conversion Time
Sixteen ADC internal clocks are required to perform one conversion. The ADC starts a conversion on the
first rising edge of the ADC internal clock immediately following a write to the ADSCR. If the ADC internal
clock is selected to run at 1 MHz, then one conversion will take 16 μs to complete. But since the ADC can
run almost completely asynchronously to the bus clock, (for example, the ADC is configured to derive its
internal clock from CGMXCLK and the bus clock is being derived from the PLL within the CGM
56
INTERNAL DATA BUS
Inside the ADC module, the reference voltage, V
ADC analog power V
ground V
analog supply voltages
For operation, V
separate traces
AIEN
INTERRUPT
LOGIC
REFL
READ DDRBx
WRITE DDRBx
WRITE PTBx
READ PTBx
DDAD
COCO
,
the ADC converts it to $00. Input voltages between V
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
CONVERSION
. Therefore, the ADC input voltage should not exceed the
BUS CLOCK
COMPLETE
RESET
CGMXCLK
DDAD
Figure 5-1. ADC Block Diagram
DDAD
should be tied to the same potential as V
ADIV2–ADIV0
; and V
ADC DATA REGISTER
REFH
GENERATOR
DDRBx
PTBx
CLOCK
ADC
REFL
NOTE
, the ADC converts the signal to $FF (full scale). If the
ADC CLOCK
ADICLK
is connected to the ADC analog
VOLTAGE IN
(V
REFH
ADC
ADIN
)
DISABLE
is connected to the
DISABLE
CHANNEL
SELECT
ADC CHANNEL x
DD
PTBx
via
ADCH4–ADCH0
REFH
Freescale Semiconductor
and V
REFH
REFL
.
are a