
Analog-to-Digital (A/D) Converter
Multiple-Channel Operation
MC68HC11E Family
—
Rev. 4
Technical Data
MOTOROLA
Analog-to-Digital (A/D) Converter
217
10.8 Multiple-Channel Operation
The two types of multiple-channel operation are:
1.
When SCAN = 0, a selected group of four channels is converted
one time each. The first result is stored in A/D result register 1
(ADR1), and the fourth result is stored in ADR4. After the fourth
conversion is complete, all conversion activity is halted until a new
conversion command is written to the ADCTL register.
2.
When SCAN = 1, conversions continue to be performed on the
selected group of channels with the fifth conversion being stored
in register ADR1 (replacing the earlier conversion result for the
first channel in the group), the sixth conversion overwriting ADR2,
and so on.
10.9 Operation in Stop and Wait Modes
If a conversion sequence is in progress when either the stop or wait
mode is entered, the conversion of the current channel is suspended.
When the MCU resumes normal operation, that channel is resampled
and the conversion sequence is resumed. As the MCU exits wait mode,
the A/D circuits are stable and valid results can be obtained on the first
conversion. However, in stop mode, all analog bias currents are disabled
and it is necessary to allow a stabilization period when leaving stop
mode. If stop mode is exited with a delay (DLY = 1), there is enough time
for these circuits to stabilize before the first conversion. If stop mode is
exited with no delay (DLY bit in OPTION register = 0), allow 10 ms for
the A/D circuitry to stabilize to avoid invalid results.