PXS20RM Datasheet, PDF (202/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Analog-to-Digital Converter (ADC)
Error interrupts related to Self Testing are handled by status bits in STSR1 and mask bits in STCR2
registers. If an error is generated due to analog watchdog monitoring or sequence checking of algorithm
or internal watchdog timer timeout, corresponding error bit is set in STSR1. The mask bits for these error
bits are present in STCR2 register.
9.4.9 Power-down mode
The analog part of the ADC can be put in a low-power mode, called “power-down mode,” by setting the
MCR[PWDN] bit. After releasing the reset signal the ADC analog module is kept in power-down mode
by default, so this state must be exited before starting any operation by clearing the appropriate bit in the
MCR.
The power-down mode can be requested at any time by setting the MCR[PWDN] bit. If a conversion is
ongoing, the ADC hard macrocell cannot immediately enter the power-down mode. In fact, the ADC
enters power-down mode only after completing the ongoing conversion. Otherwise, the ongoing operation
should be aborted manually by clearing the NSTART bit and using the ABORTCHAIN bit.
Bit ADCSTATUS[0] in the MSR is set only when ADC enters power-down mode.
After the power-down phase is completed, the process that was occurring before the power-down phase
must be restarted manually (by setting the appropriate START bit).
After an exit from power-down mode, the first conversion can be started after 5 s, otherwise the result
can be affected by the improper setting of the ADC analog operating point.
CAUTION
You must not clear the MCR[PWDN] and set the MCR[NSTART] or
MCR[JSTART] bits during the same cycle.
See also Section 9.3.12, Power Down Exit Delay Register (PDEDR).
9.4.10 Auto-clock-off mode
To reduce power consumption during the IDLE mode of operation (without going into power-down mode),
an “auto-clock-off” feature can be enabled by setting the MCR[ACKO] bit. When enabled, the analog
clock is automatically switched off when no operation is ongoing, that is, no conversion is programmed
by the user.
9.4.11 Self testing
9.4.11.1 General operation
For safety devices used for very critical applications, it is important to check at regular intervals if the ADC
is functioning correctly. For this purpose, Self Testing feature has been incorporated inside the ADC.
The self-tests use analog watchdogs to verify the result of self-test conversions. The threshold of these
watchdogs is saved in the test flash. Before running the self test, you must copy these values from the test
flash to the STAWxR registers.
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PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor