UPD78F1502AGK-GAK-AX Datasheet, PDF (374/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 7 REAL-TIME COUNTER
(13) 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
(reference value: 7FFFH) that overflows from the sub-count register (RSUBC) to the second count register.
Rewrite the SUBCUD register after disabling interrupt servicing INTRTC by using the interrupt mask flag register.
Furthermore, after rewriting the SUBCUD register, enable interrupt servicing after clearing the interrupt request
flag (RTCIF) and constant-period interrupt status flag (RIFG).
SUBCUD can be set by an 8-bit memory manipulation instruction.
Reset signal generation clears this register to 00H.
Figure 7-14. Format of Watch Error Correction Register (SUBCUD)
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
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
The range of value that can be corrected by using the watch error correction register (SUBCUD) is shown below.
Correctable range
Maximum excludes
quantization error
Minimum resolution
DEV = 0 (correction every 20 seconds)
−189.2 ppm to 189.2 ppm
±1.53 ppm
DEV = 1 (correction every 60 seconds)
−63.1 ppm to 63.1 ppm
±0.51 ppm
±3.05 ppm
±1.02 ppm
Remark If a correctable range is −63.1 ppm or lower and 63.1 ppm or higher, set 0 to DEV.
R01UH0004EJ0501 Rev.5.01
358
Jun 20, 2011