set in ACMP_C1[DACVAL] to a stepped analog output, which is fed into ACMP as an
internal reference input. This stepped analog output is also mapped out of the module.
The output voltage range is from V
in
/64 to V
in
. The step size is V
in
/64.
The ACMP can achieve the analog comparison between positive input and negative
input, and then give out a digital output and relevant interrupt. Both the positive and
negative input of ACMP can be selected from the four common inputs: three external
reference inputs and one internal reference input from the DAC output. The positive input
of ACMP is selected by ACMP_C0[ACPSEL] and the negative input is selected by
ACMP_C0[ACNSEL]. Any pair of the eight inputs can be compared by configuring the
ACMPC0 with the appropriate value.
After the ACMP is enabled by setting ACMP_CS[ACE], the comparison result appears
as a digital output. Whenever a valid edge defined in ACMP_CS[ACMOD] occurs,
ACMP_CS[ACF] is asserted. If ACMP_CS[ACIE] is set, a ACMP CPU interrupt occurs.
The valid edge is defined by ACMP_CS[ACMOD]. When ACMP_CS[ACMOD] = 00b
or 10b, only the falling-edge on ACMP output is valid. When ACMP_CS[ACMOD] =
01b, only rising-edge on ACMP output is valid. When ACMP_CS[ACMOD] = 11b, both
the rising-edge and falling-edge on the ACMP output are valid.
The ACMP output is synchronized by the bus clock to generate ACMP_CS[ACO] so that
the CPU can read the comparison. In stop3 mode, if the output of ACMP is changed,
ACMPO cannot be updated in time. The output can be synchronized and
ACMP_CS[ACO] can be updated upon the waking up of the CPU because of the
availability of the bus clock. ACMP_CS[ACO] changes following the comparison result,
so it can serve as a tracking flag that continuously indicates the voltage delta on the
inputs.
If a reference input external to the chip is selected as an input of ACMP, the
corresponding ACMP_C2[ACIPE] bit must be set to enable the input from pad interface.
If the output of the ACMP needs to be put onto the external pin, the ACMP_CS[ACOPE]
bit must enable the ACMP pin function of pad logic.
16.5 Setup and operation of ACMP
The two parts of ACMP (DAC and CMP) can be set up and operated independently. But
if the DAC works as an input of the CMP, the DAC must be configured before the
ACMP is enabled.
Chapter 16 Analog comparator (ACMP)
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
NXP Semiconductors
333
Summary of Contents for MC9S08PA4
Page 1: ...MC9S08PA4 Reference Manual Supports MC9S08PA4 Document Number MC9S08PA4RM Rev 5 08 2017 ...
Page 2: ...MC9S08PA4 Reference Manual Rev 5 08 2017 2 NXP Semiconductors ...
Page 22: ...MC9S08PA4 Reference Manual Rev 5 08 2017 22 NXP Semiconductors ...
Page 28: ...System clock distribution MC9S08PA4 Reference Manual Rev 5 08 2017 28 NXP Semiconductors ...
Page 150: ...Port data registers MC9S08PA4 Reference Manual Rev 5 08 2017 150 NXP Semiconductors ...
Page 196: ...Human machine interfaces HMI MC9S08PA4 Reference Manual Rev 5 08 2017 196 NXP Semiconductors ...
Page 224: ...Instruction Set Summary MC9S08PA4 Reference Manual Rev 5 08 2017 224 NXP Semiconductors ...
Page 232: ...Functional Description MC9S08PA4 Reference Manual Rev 5 08 2017 232 NXP Semiconductors ...
Page 258: ...FTM Interrupts MC9S08PA4 Reference Manual Rev 5 08 2017 258 NXP Semiconductors ...
Page 294: ...Functional description MC9S08PA4 Reference Manual Rev 5 08 2017 294 NXP Semiconductors ...
Page 398: ...Resets MC9S08PA4 Reference Manual Rev 5 08 2017 398 NXP Semiconductors ...
Page 400: ...MC9S08PA4 Reference Manual Rev 5 08 2017 400 NXP Semiconductors ...