HCS08 datasheet(232/290 Pages) MOTOROLA

232 / 290 page

Analog-to-Digital Converter (ATD) Module

MC9S08GB/GT

232

MOTOROLA

The effect of the DJM bit on the result is shown in Table 14-3.

1 = Result register data is right justified.

0 = Result register data is left justified.

RES8 — ATD Resolution Select

This bit determines the resolution of the ATD converter, 8-bits or 10-bits. The ATD converter has the

accuracy of a 10-bit converter. However, if 8-bit compatibility is required, selecting 8-bit resolution

will map result data bits 9-2 onto ATDRH bits 7-0.

The effect of the RES8 bit on the result is shown in Table 14-3.

1 = 8-bit resolution selected.

0 = 10-bit resolution selected.

SGN — Signed Result Select

This bit determines whether the result will be signed or unsigned data. Signed data is represented as

2’s complement data and is achieved by complementing the MSB of the result. Signed data mode can

be used only when the result is left justified (DJM = 0) and is not available for right-justified mode

(DJM = 1). When a signed result is selected, the range for conversions becomes –512 ($200) to 511

($1FF) for 10-bit resolution and –128 ($80) to 127 ($7F) for 8-bit resolution.

The effect of the SGN bit on the result is shown in Table 14-3.

1 = Left justified result data is signed.

0 = Left justified result data is unsigned.

Table 14-3 Available Result Data Formats

PRS — Prescaler Rate Select

This field of bits determines the prescaled factor for the ATD conversion clock. Table 14-4 illustrates

the divide-by operation and the appropriate range of bus clock frequencies.

RES8

DJM

SGN

Data Formats of Result

Analog Input

VREFH =VDDA,

VREFL =VSSA

ATDRH:ATDRL

VDDA

VSSA

8-bit : left justiﬁed : unsigned

$FF:$00

$00:$00

8-bit : left justiﬁed : signed

$7F:$00

$80:$00

X(1)

NOTES:

1. The SGN bit is only effective when DJM = 0. When DJM = 1, SGN is ignored.

8-bit : left justiﬁed(2) : unsigned

2. 8-bit results are always in ATDRH.

$FF:$00

$00:$00

10-bit : left justiﬁed : unsigned

$FF:$C0

$00:$00

10-bit : left justiﬁed : signed

$7F:$C0

$80:$00

10-bit : right justiﬁed : unsigned

$03:$FF

$00:$00

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