MC68711E20CFNE3 Datasheet, PDF (60/242 Pages) –

Analog-to-Digital (A/D) Converter
3.3 A/D Converter Power-Up and Clock Select
Bit 7 of the OPTION register controls A/D converter power-up. Clearing ADPU removes power from and
disables the A/D converter system. Setting ADPU enables the A/D converter system. Stabilization of the
analog bias voltages requires a delay of as much as 100 µs after turning on the A/D converter. When the
A/D converter system is operating with the MCU E clock, all switching and comparator operations are
inherently synchronized to the main MCU clocks. This allows the comparator output to be sampled at
relatively quiet times during MCU clock cycles. Since the internal RC oscillator is asynchronous to the
MCU clock, there is more error attributable to internal system clock noise. A/D converter accuracy is
reduced slightly while the internal RC oscillator is being used (CSEL = 1).
Address: $1039
Bit 7
6
5
4
3
Read:
ADPU
CSEL
IRQE⁽¹⁾
DLY⁽¹⁾
CME
Write:
2
1
Bit 0
CR1⁽¹⁾
CR0⁽¹⁾
Reset: 0
0
0
1
0
0
0
0
1. Can be written only once in first 64 cycles out of reset in normal modes or at any time in special modes
= Unimplemented
Figure 3-4. System Configuration Options Register (OPTION)
ADPU — A/D Power-Up Bit
0 = A/D powered down
1 = A/D powered up
CSEL — Clock Select Bit
0 = A/D and EEPROM use system E clock.
1 = A/D and EEPROM use internal RC clock.
IRQE — Configure IRQ for Edge-Sensitive Only Operation
Refer to Chapter 5 Resets and Interrupts.
DLY — Enable Oscillator Startup Delay Bit
0 = The oscillator startup delay coming out of stop is bypassed and the MCU resumes processing
within about four bus cycles.
1 = A delay of approximately 4000 E-clock cycles is imposed as the MCU is started up from the stop
power-saving mode. This delay allows the crystal oscillator to stabilize.
CME — Clock Monitor Enable Bit
Refer to Chapter 5 Resets and Interrupts.
Bit 2 — Not implemented
Always reads 0
CR[1:0] — COP Timer Rate Select Bits
Refer to Chapter 5 Resets and Interrupts and Chapter 9 Timing Systems.
M68HC11E Family Data Sheet, Rev. 5.1
60
Freescale Semiconductor