MC68HC16Z1 Datasheet, PDF (190/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series

Freescale Semiconductor, Inc.
STOP is set during system reset, and must be cleared before the ADC can be used.
Because analog circuit bias currents are turned off during low-power stop mode, the
ADC requires recovery time after STOP is cleared.
Execution of the CPU16 LPSTOP command places the entire modular microcontroller
in low-power stop mode. Refer to 5.3.4 Low-Power Operation for more information.
8.5.2 Freeze Mode
When the CPU16 in the modular microcontroller enters background debug mode, the
FREEZE signal is asserted. The type of response is determined by the value of the
FRZ[1:0] field in the ADCMCR. Table 8-1 shows the different ADC responses to
FREEZE assertion.
Table 8-1 FRZ Field Selection
FRZ[1:0]
00
01
10
11
Response
Ignore FREEZE, continue conversions
Reserved
Finish conversion in process, then freeze
Freeze immediately
When the ADC freezes, the ADC clock stops and all sequential activity ceases.
Contents of control and status registers remain valid while frozen. When the FREEZE
signal is negated, ADC activity resumes.
If the ADC freezes during a conversion, activity resumes with the next step in the con-
version sequence. However, capacitors in the analog conversion circuitry discharge
while the ADC is frozen; as a result, the conversion will be inaccurate.
Refer to 4.14.4 Background Debug Mode for more information.
8.6 Analog Subsystem
The analog subsystem consists of a multiplexer, sample capacitors, a buffer amplifier,
an RC DAC array, and a high-gain comparator. Comparator output sequences the
successive approximation register (SAR). The interface between the comparator and
the SAR is the boundary between ADC analog and digital subsystems.
8.6.1 Multiplexer
The multiplexer selects one of 16 sources for conversion. Eight sources are internal
and eight are external. Multiplexer operation is controlled by channel selection field
CD:CA in register ADCTL1. Table 8-2 shows the different multiplexer channel
sources. The multiplexer contains positive and negative stress protection circuitry.
This circuitry prevents voltages on other input channels from affecting the current con-
version.
ANALOG-TO-DIGITAL CONVERTER
M68HC16 Z SERIES
8-4
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