9 REAL-TIME CLOCK (RTCA)
S1C17M20/M21/M22/M23/M24/M25
Seiko Epson Corporation
9-7
TECHNICAL MANUAL (Rev. 1.0)
Note
: When the RTCCTL.RTCTRMBSY bit = 1, the RTCCTL.RTCHLD bit cannot be rewritten to 1
(as fixed at 0).
Bit 4
RTC24H
This bit sets the hour counter to 24H mode or 12H mode.
1 (R/W): 24H mode
0 (R/W): 12H mode
This selection changes the count range of the hour counter. Note, however, that the counter value is
not updated automatically, therefore, it must be programmed again.
Note
: Be sure to avoid writing to this bit when the RTCCTL.RTCRUN bit = 1.
Bit 3
Reserved
Bit 2
RTCADJ
This bit executes the 30-second correction time adjustment function.
1 (W):
Execute 30-second correction
0 (W):
Ineffective
1 (R):
30-second correction is executing.
0 (R):
30-second correction has finished. (Normal operation)
Writing 1 to this bit executes 30-second correction and an enabled interrupt occurs even if the RT-
CCTL.RTCRUN bit = 0. The correction takes up to 2/256 seconds. The RTCCTL.RTCADJ bit is
automatically cleared to 0 when the correction has finished. For more information on the 30-second
correction, refer to “Real-Time Clock Counter Operations.”
Notes: • Be sure to avoid writing to this bit when the RTCCTL.RTCBSY bit = 1.
• Do not write 1 to this bit again while the RTCCTL.RTCADJ bit = 1.
Bit 1
RTCRST
This bit resets the 1 Hz counter, the RTCCTL.RTCADJ bit, and the RTCCTL.RTCHLD bit.
1 (W):
Reset
0 (W):
Ineffective
1 (R):
Reset is being executed.
0 (R):
Reset has finished. (Normal operation)
This bit is automatically cleared to 0 after reset has finished.
Bit 0
RTCRUN
This bit starts/stops the real-time clock counter.
1 (R/W): Running/start control
0 (R/W): Idle/stop control
When the real-time clock counter stops counting by writing 0 to this bit, the counter retains the value
when it stopped. Writing 1 to this bit again resumes counting from the value retained.
RTC Second Alarm Register
Register name
Bit
Bit name
Initial
Reset
R/W
Remarks
RTCALM1
15 –
0
–
R
–
14–12 RTCSHA[2:0]
0x0
H0
R/W
11–8 RTCSLA[3:0]
0x0
H0
R/W
7–0 –
0x00
–
R
Bit 15
Reserved
Bits 14–12 RTCSHA[2:0]
Bits 11–8 RTCSLA[3:0]
The RTCALM1.RTCSHA[2:0] bits and the RTCALM1.RTCSLA[3:0] bits set the 10-second digit and
1-second digit of the alarm time, respectively. A value within 0 to 59 seconds can be set in BCD code
as shown in Table 9.6.1.