RL78/G1H CHAPTER 9 REAL-TIME CLOCK
R01UH0575EJ0120 Rev. 1.20 Page 250 of 920
Dec 22, 2016
9.3.12 Watch error correction register (SUBCUD)
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.
Figure 9 - 14 Format of Watch error correction register (SUBCUD)
The range of value that can be corrected by using the watch error correction register (SUBCUD) is shown below.
Remark If a correctable range is −63.1 ppm or lower and 63.1 ppm or higher, set 0 to DEV.
Address: FFF99H After reset: 00H R/W
Symbol76543210
SUBCUDDEVF6F5F4F3F2F1F0
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
0 Increases by {(F5, F4, F3, F2, F1, F0) – 1}
× 2.
1 Decreases by {(/F5, /F4, /F3, /F2, /F1, /F0) + 1}
× 2.
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
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
Maximum excludes
quantization error
±1.53 ppm ±0.51 ppm
Minimum resolution
±3.05 ppm ±1.02 ppm
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