MC68HC705MC4 Datasheet, PDF (50/99 Pages) Motorola, Inc – Microcontrollers

MC68HC705MC4 Specification Rev. 1.5
7.4.2 ADRC - A/D RC OSCILLATOR CONTROL
When the RC oscillator is selected (ADRC = 1) to be the A/D clock source, it requires a
time t_ADRC to stabilize. Results can be inaccurate during this time. If the CPU clock is
running below 1 Mhz, the RC oscillator must be used.
When ADRC=0, the A/D uses the CPU clock.
7.4.3 ADON - A/D ON
When the A/D is turned on (ADON = 1), it requires a time t_ADON for the current sources to
stabilize, and results can be inaccurate during this time. This bit turns on the charge pump.
If the ADRC is set, clearing this bit disables the RC oscillator to save power.
7.4.4 CH3:CH0 - CHANNEL SELECT BITS
CH3, CH2, CH1, and CH0 form a 4-bit field, which is used to select one of eight A/D
channels. Channels 0-5 correspond to Port C input pins on the MCU. Channels 8-a are
used for internal reference points. In User Mode, channel b is reserved and converts to
$00. The following table shows the signals selected by the channel select field.
Using a Port C pin as both an analog and digital input simultaneously is prohibited to
prevent excess power dissipation. When the A/D is enabled (ADON = 1) and one of the
channels 0-5 is selected, the corresponding Port C pin will appear as a logic zero to a
digital read. The remaining Port C pins (0-5) will read normally. To digitally read all eight
Port C pins simultaneously, the A/D must be disabled (ADON = 0).
Section 7: Analog Subsystem
MOTOROLA
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