Renesas rl78 User Manual

 

RL78/G1A 

 

CHAPTER  7   REAL-TIME  CLOCK 

This register is used to correct the watch with high accuracy when it is slow or fast by changing the value that overflows 

from the internal counter (16-bit) to the second count register (SEC) (reference value: 7FFFH). 

The SUBCUD register can be set by an 8-bit memory manipulation instruction. 

Reset signal generation clears this register to 00H. 

 

 

Address: FFF99H     After reset: 00H     R/W 

Symbol 

7 6 5 4 3 2 1 0 

SUBCUD 

DEV 

F6 F5 F4 F3 F2 F1 F0 

 

DEV 

Setting of watch error correction timing 

0 

Corrects watch error when the second digits are at 00, 20, or 40 (every 20 seconds). 

1 

Corrects watch error only when the second digits are at 00 (every 60 seconds). 

Writing to the SUBCUD register at the following timing is prohibited. 

• When DEV = 0 is set: For a period of SEC = 00H, 20H, 40H 

• When DEV = 1 is set: For a period of SEC = 00H 

 

F6 

Setting of watch error correction value 

Increases by {(F5, F4, F3, F2, F1, F0) – 1} 

× 2. 

0 

Decreases by {(/F5, /F4, /F3, /F2, /F1, /F0) + 1} 

× 2. 

1 

When (F6, F5, F4, F3, F2, F1, F0) = (*, 0, 0, 0, 0, 0, *), the watch error is not corrected.  * is 0 or 1. 

/F5 to /F0 are the inverted values of the corresponding bits (000011 when 111100). 

Range of correction value:  (when F6 = 0)   2, 4, 6, 8, … , 120, 122, 124 

 

(when F6 = 1)   –2, –4, –6, –8, … , –120, –122, –124 

 

The range of value that can be corrected by using the watch error correction register (SUBCUD) is shown below. 

 

 

DEV = 0 (correction every 20 seconds) 

DEV = 1 (correction every 60 seconds) 

Correctable range 

–189.2 ppm to 189.2 ppm 

–63.1 ppm to 63.1 ppm 

± 1.53 ppm 

± 0.51 ppm 

Maximum excludes 

quantization error 

± 3.05 ppm 

± 1.02 ppm 

Minimum resolution 

 

Remark  If a correctable range is –63.1 ppm or lower and 63.1 ppm or higher, set 0 to DEV.  

R01UH0305EJ0200  Rev.2.00 

 

 

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Jul 04, 2013