AN974 datasheet(2/6 Pages) STMICROELECTRONICS

部件名	AN974

功能描述	Real time clock with ST7 Timer Output Compare

PDF	6 Pages

Scroll/Zoom	100%

制造商	STMICROELECTRONICS [STMicroelectronics]

网页	http://www.st.com

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Real time clock with ST7 Timer Output Compare

Figure 1. Output Compare Register Update Flowchart

Based on the assumption that fCPU is 4-MHz, Table 1 gives some basic possible time bases

with the Output compare register offset value (OCxHR, OCxLR).

(OCxHR OCxLR )offset =

3 REAL TIME CLOCK APPLICATION

The real time clock application is based on four software counters (100ms, seconds, minutes

and hours) updated by a 100ms ST7 timer output compare 1 interrupt.

Table 1. Output Compare Register and Timebase Values with ftimercnt at 500KHz

Time Base [ms]

100

131.07

OCxHR OCxLR offset [hex]

03E8

1388

2710

61A8

C350

FFFF

STORE OCxHR AND OCxLR REGISTER

VALUES IN TEMPORARY REGISTERS

UPDATE OCxHR AND OCxLR VALUES

THROUGH TEMPORARY REGISTERS

STORE NEW OCxHR REGISTER VALUE

STORE NEW OCxLR REGISTER VALUE

ftimercnt =

fCPU

(cc1,cc0)

4 MHz

= 500 KHz

Ttimercnt = 2 us

TimeBase

Ttimercnt

TimeBase

2 us

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