MC705P6ACPE Datasheet, PDF (55/98 Pages) Freescale Semiconductor, Inc – M68HC05 Microcontrollers

A/D Conversion Data Register (ADC)
ADRC — RC Oscillator Control
When ADRC is set, the A/D subsystem operates from the internal RC oscillator instead of the internal
clock. The RC oscillator requires a time, t_RCON, to stabilize before accurate conversion results can be
obtained. See 9.2.2 Reference Voltage (VREFH) for more information.
ADON — A/D Subsystem On
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.
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 for factory test
9.6 A/D Conversion Data Register (ADC)
This register contains the output of the A/D converter. See Figure 9-2.
Address: $001D
Bit 7
6
5
4
3
2
1
Bit 0
Read: AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
Write:
Reset:
Unaffected by reset
= Unimplemented
Figure 9-2. A/D Conversion Value Data Register (ADC)
MC68HC705P6A Advance Information Data Sheet, Rev. 2.1
Freescale Semiconductor
55