PFS172 datasheet(29/92 Pages) PADAUK

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PFS172

8bit MTP MCU with 8-bit ADC

Page 29 of 92

PDK-DS-PFS172-EN_V000-May 8, 2020

5.3. Data Memory - SRAM

The access of data memory can be byte or bit operation. Besides data storage, the SRAM data memory is

also served as data pointer of indirect access method and the stack memory.

The stack memory is defined in the data memory. The stack pointer is defined in the stack pointer register; the

depth of stack memory of each processing unit is defined by the user. The arrangement of stack memory fully

flexible and can be dynamically adjusted by the user.

For indirect memory access mechanism, the data memory is used as the data pointer to address the data

byte. All the data memory could be the data pointer; it’s quite flexible and useful to do the indirect memory

access. Since the data width is 8-bit, all the 128 bytes data memory of PFS172 can be accessed by indirect

access mechanism.

5.4. Oscillator and clock

There are three oscillator circuits provided by PFS172: external crystal oscillator (EOSC), internal high RC

oscillator (IHRC) and internal low RC oscillator (ILRC), and these three oscillators are enabled or disabled by

registers eoscr.7, clkmd.4 and clkmd.2 independently. User can choose one of these three oscillators as

system clock source and use clkmd register to target the desired frequency as system clock to meet different

applications.

Oscillator Module

Enable/Disable

EOSC

eoscr.7

IHRC

clkmd.4

ILRC

clkmd.2

Table 2: Three oscillation circuits

5.4.1. Internal High RC oscillator and Internal Low RC oscillator

After boot-up, the IHRC and ILRC oscillators are enabled. The frequency of IHRC can be calibrated to

eliminate process variation by ihrcr register; normally it is calibrated to 16MHz. Please refer to the

measurement chart for IHRC frequency verse VDD and IHRC frequency verse temperature.

The frequency of ILRC will vary by process, supply voltage and temperature, please refer to DC specification

and do not use for accurate timing application.

5.4.2. Chip calibration

The IHRC frequency and bandgap reference voltage may be different chip by chip due to manufacturing

variation, PFS172 provide the IHRC frequency calibration to eliminate this variation, and this function can be

selected when compiling user’s program and the command will be inserted into user’s program automatically.

The calibration command is shown as below:

.ADJUST_IC SYSCLK=IHRC/(p1), IHRC=(p2)MHz, VDD=(p3)V;

Where, p1=2, 4, 8, 16, 32; In order to provide different system clock.

p2=14 ~ 18; In order to calibrate the chip to different frequency, 16MHz is the usually one.

p3=2.5 ~ 5.5; In order to calibrate the chip under different supply voltage.

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