MC68HC05P18 Datasheet, PDF (83/144 Pages) Freescale Semiconductor, Inc – Advance Information

Freescale Semiconductor, Inc.
Analog-to-Digital (A/D) Converter
A/D Status and Control Register
ADON — A/D Subsystem On But
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 which 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 will be $00. Table 9-1 lists the inputs
selected by bits CH0–CH3.
If the ADON bit is set and an input from channels 0–4 is selected, the
corresponding port C pin’s DDR bit will be 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 will read as a logic 0. The remaining port C pins
will read normally. To digitally read a port C pin, the A/D subsystem must
be disabled (ADON = 0) or input channels 5–7 must be selected.
Table 9-1. 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
MC68HC(8)05P18 — Rev. 2.0
MOTOROLA
Analog-to-Digital (A/D) Converter
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Advance Information
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