M68HC11KA datasheet(49/68 Pages) MOTOROLA

49 / 68 page

MC68HC11KA4

MOTOROLA

MC68HC11KA4TS/D

Pins AVDD and AVSS provide the supply voltage to the digital portion of the A/D converter. Pins VRH and

VRL provide the reference supply voltage inputs.

A multiplexer allows the single A/D converter to select one of 16 analog input signals. Refer to the A/D

converter channel assignment bits CD–CA description.

The A/D converter control logic implements automatic conversion sequences on a selected channel

four times or on a group of four channels once each. A write to the ADCTL register initiates conversions

and, if made while a conversion is in process, a write to ADCTL also halts a conversion operation in

progress.

When the MULT bit is zero, the A/D converter system is configured to perform four consecutive conver-

sions on the single channel specified by the four channel-select bits (CD–CA). When the MULT bit is

one, the A/D system is configured to perform conversions on each channel in the group of four channels

specified by the CD and CC channel select bits. Refer to Table 8.

When the SCAN bit is zero, four conversions are performed in the desired channel group, once each,

to fill the four result registers. When SCAN is one, conversions continue channel-by-channel in the de-

sired group with the result registers being updated continually as new data becomes available.

Figure 15 Timing Diagram for a Sequence of Four A/D Conversions

Figure 16 Electrical Model of an Analog Input Pin (Sample Mode)

128 — E CYCLES

SAMPLE ANALOG INPUT

SUCCESSIVE APPROXIMATION SEQUENCE

MSB

CYCLES

BIT 6

CYC

BIT 5

CYC

BIT 4

CYC

BIT 3

CYC

BIT 2

CYC

BIT 1

CYC

LSB

CYC

END

CONVERT FIRST

CHANNEL, UPDATE

ADR1

CONVERT SECOND

CHANNEL, UPDATE

ADR2

CONVERT THIRD

CHANNEL, UPDATE

ADR3

CONVERT FOURTH

CHANNEL, UPDATE

ADR4

12 E CYCLES

E CLOCK

A/D CONVERSION TIM

DIFFUSION/POLY

< 2 pF

COUPLER

400 nA

JUNCTION

LEAKAGE

+ ~20V

– ~0.7V

* THIS ANALOG SWITCH IS CLOSED ONLY DURING THE 12-CYCLE SAMPLE TIME.

VRL

INPUT

+ ~12V

– ~0.7V

PROTECTION

DEVICE

≤ 4 KΩ

DUMMY N-CHANNEL

OUTPUT DEVICE

ANALOG

INPUT

~ 20 pF

DAC

CAPACITANCE

ANALOG INPUT PIN

M68HC11KA Datasheet(PDF) 49 Page - Motorola, Inc

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