HCS08 datasheet(216/374 Pages) NXP

216 / 374 page

Real-Time Counter (S08RTCV1)

MC9S08JM60 Series Data Sheet, Rev. 5

216

Freescale Semiconductor

13.3.2

RTC Counter Register (RTCCNT)

RTCCNT is the read-only value of the current RTC count of the 8-bit counter.

13.3.3

RTC Modulo Register (RTCMOD)

13.4

Functional Description

The RTC is composed of a main 8-bit up-counter with an 8-bit modulo register, a clock source selector,

and a prescaler block with binary-based and decimal-based selectable values. The module also contains

software selectable interrupt logic.

After any MCU reset, the counter is stopped and reset to 0x00, the modulus register is set to 0x00, and the

prescaler is off. The 1-kHz internal oscillator clock is selected as the default clock source. To start the

prescaler, write any value other than zero to the prescaler select bits (RTCPS).

Three clock sources are software selectable: the low power oscillator clock (LPO), the external clock

(ERCLK), and the internal clock (IRCLK). The RTC clock select bits (RTCLKS) select the desired clock

source. If a different value is written to RTCLKS, the prescaler and RTCCNT counters are reset to 0x00.

432

RTCCNT

Reset:

Figure 13-4. RTC Counter Register (RTCCNT)

Table 13-4. RTCCNT Field Descriptions

Field

Description

7:0

RTCCNT

RTC Count. These eight read-only bits contain the current value of the 8-bit counter. Writes have no effect to this

432

RTCMOD

Reset:

Figure 13-5. RTC Modulo Register (RTCMOD)

Table 13-5. RTCMOD Field Descriptions

Field

Description

7:0

RTCMOD

RTC Modulo. These eight read/write bits contain the modulo value used to reset the count to 0x00 upon a compare

match and set the RTIF status bit. A value of 0x00 sets the RTIF bit on each rising edge of the prescaler output.

Writing to RTCMOD resets the prescaler and the RTCCNT counters to 0x00. Reset sets the modulo to 0x00.

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