Renesas rl78 User Manual

 

RL78/G1A 

 

CHAPTER  7   REAL-TIME  CLOCK 

The watch can be corrected with high accuracy when it is slow or fast, by setting a value to the watch error correction 

register. 

 

Example of calculating the correction value  

The correction value used when correcting the count value of the internal counter (16-bit) is calculated by using the 

following expression. 

Set the DEV bit to 0 when the correction range is 

−63.1 ppm or less, or 63.1 ppm or more. 

 

(When DEV = 0) 

 = Number of correction counts in 1 minute 

÷ 3 = (Oscillation frequency ÷ Target frequency − 1) 

¯ 32768 ¯ 60 

÷ 3 

Correction value

 

(When DEV = 1) 

 = Number of correction counts in 1 minute = (Oscillation frequency 

÷ Target frequency − 1) ¯ 

32768 

¯ 60 

Correction value

 

Note  The correction value is the watch error correction value calculated by using bits 6 to 0 of the watch error 

correction register (SUBCUD). 

(When F6 = 0)  Correction value = {(F5, F4, F3, F2, F1, F0) 

− 1} ¯ 2 

(When F6 = 1)  Correction value = 

− {(/F5, /F4, /F3, /F2, /F1, /F0) + 1} ¯ 2 

 

When (F6, F5, F4, F3, F2, F1, F0) is (*, 0, 0, 0, 0, 0, *), watch error correction is not performed.  “*” is 0 or 1. 

/F5 to /F0 are bit-inverted values (000011 when 111100). 

 

Remarks  1.  The correction value is 2, 4, 6, 8, … 120, 122, 124 or 

−2, −4, −6, −8, … −120, −122, −124. 

2.  The oscillation frequency is a value of the count clock (f

RTC

). 

It can be calculated from the output frequency of the RTC1HZ pin 

¯ 32768 when the watch error 

correction register is set to its initial value (00H). 

3.   The target frequency is the frequency resulting after correction performed by using the watch error 

correction register. 

 

R01UH0305EJ0200  Rev.2.00 

 

 

316  

Jul 04, 2013