MC68HC05P18A Datasheet, PDF (95/130 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog-to-Digital (A/D) Converter
A/D Status and Control Register
R — Reserved Bit
This bit is not currently used. It can be read or written, but does not
control anything.
ADON — A/D Subsystem On Bit
When the A/D subsystem is turned on (ADON = 1), it requires a time
t_ADON to stabilize before accurate conversion results can be attained.
CH2–CH0 — Channel Select Bits
CH2, CH1, and CH0 form a 3-bit field that is used to select an input to
the A/D converter. Channels 0–3 correspond to port C input pins
PC6–PC3. Channels 4–6 are used for reference measurements. In
user mode, channel 7 is reserved. If a conversion is attempted with
channel 7 selected, the result is $00. Table 11-1 lists the inputs
selected by bits CH0–CH3.
Table 11-1. A/D Multiplexer Input
Channel Assignments
Channel
0
1
2
3
4
5
6
7
Signal
AD0 port C bit 6
AD1 port C bit 5
AD2 port C bit 4
AD3 port C bit 3
V_REFH port C bit 7
(V_REFH + V_SS)/2
V_SS
Reserved
If the ADON bit is set, and an input from channels 0–4 is selected, the
corresponding port C pin’s DDR bit is cleared (making that port C pin
an input). If the port C data register is read while the A/D is on, and
one of the shared input channels is selected using bit CH0–CH2, the
corresponding port C pin reads as a logic 0. The remaining port C pins
read normally. To digitally read a port C pin, the A/D subsystem must
be disabled (ADON = 0) or input channel 5–7 must be selected.
MC68HC05P18A
Analog-to-Digital (A/D) Converter
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Technical Data