XC912BC32CFU8 Motorola Semiconductor Products, XC912BC32CFU8 Datasheet - Page 306

• Manufacturer Part Number: XC912BC32CFU8
• Description: M68HC12B Family Data Sheet
• Manufacturer: Motorola Semiconductor Products

Analog-to-Digital Converter (ATD)
Data Sheet
306
PRS4–PRS0 — Select Divide-By Factor for ATD P-Clock Prescaler Bits
SMP1
The binary value written to these bits (1 to 31) selects the divide-by factor for the
modulo counter-based prescaler. The P clock is divided by this value plus one,
and then fed into a divide-by-two circuit to generate the ATD module clock. The
divide-by-two circuit ensures symmetry of the output clock signal. Clearing
these bits causes the prescale value to default to 1 which results in a
divide-by-two prescale factor. This signal is then fed into the divide-by-two logic.
The reset state divides the P clock by a total of four and is appropriate for
nominal operation at a bus rate of between 2 MHz and 8 MHz.
shows the divide-by operation and the appropriate range of system clock
frequencies.
0
0
1
1
1. Maximum conversion frequency is 2 MHz. Maximum P clock divisor value becomes
2. Minimum conversion frequency is 500 kHz. Minimum P clock divisor value becomes
Prescale Value
maximum conversion rate that can be used on this ATD module.
minimum conversion rate that this ATD can perform.
SMP0
00000
00001
00010
00011
00100
00101
00110
00111
01xxx
1xxxx
0
1
0
1
Analog-to-Digital Converter (ATD)
16 ATD clock periods
2 ATD clock periods
4 ATD clock periods
8 ATD clock periods
Table 17-2. Final Sample Time Selection
Sample Time
Table 17-3. Clock Prescaler Values
Final
Total Divisor
10
12
14
16
2
4
6
8
18 ATD clock periods
20 ATD clock periods
24 ATD clock periods
32 ATD clock periods
Conversion Time
Max P Clock
Total 8-Bit
Do not use
4 MHz
8 MHz
8 MHz
8 MHz
8 MHz
8 MHz
8 MHz
8 MHz
(1)
M68HC12B Family — Rev. 8.0
20 ATD clock periods
22 ATD clock periods
26 ATD clock periods
34 ATD clock periods
Conversion Time
Min P Clock
Total 10-Bit
Table 17-3
1 MHz
2 MHz
3 MHz
4 MHz
5 MHz
6 MHz
7 MHz
8 MHz
MOTOROLA
(2)