TMS77C82 datasheet(38/63 Pages) TI

38 / 63 page

TMS370CxCx

8-BIT MICROCONTROLLER

SPNS040B – NOVEMBER 1995 – REVISED FEBRUARY 1997

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251–1443

analog-to-digital converter 2 module (continued)

Table 28. A / D CONTROL REGISTER (ADCTL)

Bit #

P070

CONVERT

START

SAMPLE

START

—

REF VOLT

SELECT1

REF VOLT

SELECT0

—

AD INPUT

SELECT1

AD INPUT

SELECT0

RW– 0

RW – 0

R = read, W = write, –

n = value of the bit after the register is reset

Bits 0–1

AD INPUT SELECT 0–1 (analog input channel select bits 0 – 1)

These bits select the channel used for conversion. Channels should be changed only after the

ADC2 module has cleared the SAMPLE START and CONVERT START bits. Changing the

channel while either SAMPLE START or CONVERT START is 1 invalidates the conversion in

progress.

Table 29. Analog-Input Channel Selection

AD INPUT

SELECT 1

AD INPUT

SELECT 0

AD INPUT

CHANNEL

AN0

AN1

AN2

AN3

Bit 2

Reserved (read data is indeterminate)

Bits 3–4

REF VOLT SELECT 3–4 (reference voltage (+VREF) select bits 3–4)

These bits select the channel the ADC2 module uses for the positive voltage reference. These

bits must not change during the entire conversion.

Table 30. Voltage-Channel Selection

REF VOLT

SELECT 1

REF VOLT

SELECT 0

+VREF

SOURCE

VCC

AN1

AN2

AN3

Bit 5

Reserved (read data is indeterminate)

Bit 6

SAMPLE START (sample start)

Setting this bit stops any ongoing conversion and starts sampling the selected input channel to

begin a new conversion. This bit is cleared by the ADC2 module. Entering HALT or STANDBY

mode clears this bit and aborts any sampling in progress.

Bit 7

CONVERT START (conversion start)

Setting this bit starts the conversion. This bit is cleared by the ADC2 module. Entering HALT or

STANDBY mode clears this bit and aborts any conversion in progress.

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