NXP Semiconductors freescale semiconductor MC13211, Reference Manual

Page: 349 / 372

Analog to Digital (ATD) Module
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor 20-11
The effect of the RES8 bit on the result is shown in Table 20-3 .
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 20-3 .
1 = Left justified result data is signed.
0 = Left justified result data is unsigned.
PRS — Prescaler Rate Select
This field of bits determines the prescaled factor for the ATD conversion clock. Table 20-4 illustrates
the divide-by operation and the appropriate range of bus clock frequencies.
Table 20-3. Available Result Data Formats
RES8 DJM SGN Data Formats of Result
Analog Input
V
REFH
= V
DDA
, V
REFL
= V
SSA
ATD1RH:ATD1RL
V
DDA
V
SSA
1 0 0 8-bit : left justified : unsigned $FF:$00 $00:$00
1 0 1 8-bit : left justified : signed $7F:$00 $80:$00
1 1
X
1
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 ATD1RH.
$FF:$00 $00:$00
0 0 0 10-bit : left justified : unsigned $FF:$C0 $00:$00
0 0 1 10-bit : left justified : signed $7F:$C0 $80:$00
0 1
X
1
10-bit : right justified : unsigned $03:$FF $00:$00
Table 20-4. Clock Prescaler Values
PRS Factor = (PRS +1)
×
2
Max Bus Clock
MHz
(2 MHz max ATD Clock)
1
Max Bus Clock
MHz
(1 MHz max ATD Clock)
2
Min Bus Clock
3
MHz
(500 kHz min ATD Clock)
0000 2 4 2 1
0001 4 8 4 2
0010 6 12 6 3
0011 8 16 8 4
0100 10 20 10 5
0101 12 20 12 6