MC68HC705MC4MP datasheet(76/180 Pages) FREESCALE

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Analog Subsystem

MC68HC705MC4 — Rev. 2.0

Analog Subsystem

ADON — A/D On

When the A/D is turned on (ADON = 1), it requires a time tADON 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.

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. Table 8-1

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 0 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).

Table 8-1. A/D Channel Assignments

Channel

Signal

AD0 Port C Bit 0

AD1 Port C Bit 1

AD2 Port C Bit 2

AD3 Port C Bit 3

AD4 Port C Bit 4

AD5 Port C Bit 5

Unused

8VREFH

9VREFL

a(VREFH + VREFL)/2

b–f

VREFL

Freescale Semiconductor, Inc.

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