MC68HC711G5 MOTOROLA [Motorola, Inc], MC68HC711G5 Datasheet - Page 117

• Manufacturer Part Number: MC68HC711G5
• Description: High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcontroller
• Manufacturer: MOTOROLA [Motorola, Inc]

MC68HC11G5
9.4.4
Conversions continue to be performed on all eight channels with the ninth conversion being stored
in the ADR1 register (replacing the earlier conversion result for the first channel in the group), the
tenth conversion overwrites ADR2, the eleventh overwrites ADR3, and so on, continuously. Using
this second variation the data in any result register is, at most, eight conversion times old.
A/D power up is controlled by the ADPU bit in the OPTION register. When ADPU is cleared, power
to the A/D system is removed. When ADPU is set, the A/D system is enabled. A delay of 100
microseconds is required after turning on the A/D converter, to allow the analog bias voltages to
stabilize.
Clock select is controlled by the CSEL bit in the OPTION register. When CSEL is cleared, the A/D
system uses the system E-clock. When CSEL is set, the A/D system uses an internal R-C clock
source, nominally 1.5 MHz, in which case the R-C internal clock should be selected. A delay of 10
milliseconds is required, after changing CSEL from zero to one, to allow the R-C oscillator to start
and internal bias voltages to settle.
When the A/D system is operating with the MCU E-clock, all switching and comparator operations
are synchronized with the MCU clock. This allows the comparator results to be sampled at quiet
clock times to minimise the effect of internal switching noise. As the internal R-C oscillator is
asynchronous with respect to the MCU clock, internal switching noise is more likely to affect the
overall accuracy of the A/D results, when using this oscillator, than when using the E-clock.
If a conversion sequence is still in process when the MC68HC11G5 enters the STOP or WAIT mode,
the conversion of the current channel is suspended. When the MCU resumes normal operation, that
channel is re-sampled and the conversion sequence resumes. As the MCU exits the WAIT mode,
the A/D circuits are stable and valid results can be obtained on the first conversion. However, in
STOP mode the comparator, charge pump and R-C oscillator are turned off. If the MC68HC11G5
exits the STOP mode with a delay (as is normal), there will automatically be enough time for these
circuits to stabilize before the first conversion. If the MC68HC11G5 exits the STOP mode with no
delay (DLY bit in OPTION register equal to zero) and a stable external clock supplied, the user must
allow about 100 microseconds for the A/D circuitry to stabilize and to avoid invalid results.
9.5
9.6
POWER-UP AND CLOCK SELECT
OPERATION IN STOP AND WAIT MODES
8-Channel Continuous Scan
ANALOG-TO-DIGITAL CONVERTER
MOTOROLA
9-5