Functional Descriptions. Holtek HT32F5828

32-Bit Arm ®

HT32F5828

Cortex ® -M0+ MCU

Functional Descriptions

RTC Related Register Reset

The RTC registers can only be reset by either a V

Domain software reset by setting the PWRST bit in the PWRCR register. Other reset events have no effect to clear the RTC registers.

DD

Domain power on reset, POR, or by a V

DD

Reading RTC Register

The RTC control logic and the related registers are powered by the V the APB bus, which is located in the V in the V

DD15

DD

supply voltage. Therefore, the RTC circuitry remains operational in the Power-Down mode where V

DD15

is powered off. Only

domain, is interconnected to the RTC circuits located

DD

domain using level shift circuitry and isolated by the ISO signals when the V

DD15

supply voltage is powered off.

Low Speed Clock Configuration

The default RTC clock source, CK_RTC, is derived from the LSI oscillator. The CK_RTC clock can be derived from either the external 32768 Hz crystal oscillator, named the LSE oscillator, or the internal 32K RC oscillator named the LSI oscillator, by setting the RTCSRC bit in the RTCCR register. A prescaler is provided to divide the CK_RTC by a ratio ranged from 2 0 to 2 15 determined by the RPRE [3:0] field. For instance, setting the prescaler value RPRE [3:0] to 0xF will generate an exact 1 Hz CK_SECOND clock if the CK_RTC clock frequency is equal to 32,768 Hz. The

LSE oscillator can be enabled by the LSEEN control bit in the RTCCR register. In addition, the

LSE oscillator startup mode can be selected by configuring the LSESM bit in the RTCCR register.

This enables the LSE oscillator to have either a shorter startup time or a lower power consumption, both of which are traded off depending upon specific application requirements. An example of the startup time and the power consumption for different startup modes are shown in the accompanying table for reference.

Table 70. LSE Startup Mode Operating Current and Startup Time

Startup Mode

Normal startup

LSESM Setting in the RTCCR Register

0

Operating Current

2.0 μA

Startup Time

Above 500 ms

Fast startup 1 3.5 μA Below 300 ms

@ V

DD

= 3.3 V and LSE clock = 32,768 Hz; these values are only for reference, actual values are dependent on the specification of the external 32.768 kHz crystal.

Rev. 1.00 563 of 637 December 28, 2020