MC9S08RC8 Datasheet, PDF (181/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

Analog Comparator (ACMP) Block Description
14.4 Functional Description
The analog comparator can be used to compare two analog input voltages applied to ACMP1– and
ACMP1+; or it can be used to compare an analog input voltage applied to ACMP1– with an internal
bandgap reference voltage. The ACBGS bit is used to select the mode of operation. The comparator output
is high when the non-inverting input is greater than the inverting input, and is low when the non-inverting
input is less than the inverting input. The ACMOD0 and ACMOD1 bits are used to select the condition
that will cause the ACF bit to be set. The ACF bit can be set on a rising edge of the comparator output, a
falling edge of the comparator output, or either a rising or a falling edge. The comparator output can be
read directly through the ACO bit.
14.4.1 Interrupts
The ACMP module is capable of generating an interrupt on a compare event. The interrupt request is
asserted when both the ACIE bit and the ACF bit are set. The interrupt is deasserted by clearing either the
ACIE bit or the ACF bit. The ACIE bit is cleared by writing a 0 and the ACF bit is cleared by writing a 1.
14.4.2 Wait Mode Operation
During wait mode the ACMP, if enabled, will continue to operate normally. Also, if enabled, the interrupt
can wake up the MCU.
14.4.3 Stop Mode Operation
During stop mode, clocks to the ACMP module are halted. The ACMP comparator circuit will enter a low
power state. No compare operation will occur while in stop mode.
In stop1 and stop2 modes, the ACMP module will be in its reset state when the MCU recovers from the
stop condition and must be re-initialized.
In stop3 mode, control and status register information is maintained and upon recovery normal ACMP
function is available to the user.
14.4.4 Background Mode Operation
When the microcontroller is in active background mode, the ACMP will continue to operate normally.
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
Freescale Semiconductor
181