8 REAL-TIME CLOCK (RTC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
8-15
When a value of 1 is read from RTCBSY after writing 1 to RTCHLD, it means that carry is taking
place. In this case, writing 1 to RTCHLD is ignored and RTCHLD retains 0. A period of 4 ms per
second is required for a carry over of 1 to the counters. In this case, repeat writing 1 to RTCHLD and
checking RTCBSY, or write 1 to RTCHLD and check RTCBSY after waiting for 4 ms.
D0
RTCHLD: Counter Hold Control Bit
This bit allows the busy state of counters to be checked and the counters held intact.
1 (R/W): Checks for busy state/Holds counters
0 (R/W): Normal operation (software reset value)
For the operation of this bit, see the description of RTCBSY above.
RTC Second Register (RTC_SEC)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
RTC Second
Register
(RTC_SEC)
0x300a04
(8 bits)
D7
–
reserved
–
–
–
0 when being read.
D6–4 RTCSH[2:0] RTC 10-second counter
0 to 5
X (
*
) R/W
D3–0 RTCSL[3:0] RTC 1-second counter
0 to 9
X (
*
) R/W
*
Software reset (RTCRST
→
1
→
0) does not affect the counter values. This register retains the value set before a software reset is
performed.
Note: Data should not be read from or written to the counters while 1 is being carried over. (See Section
8.3.5, “Counter Hold and Busy Flag,” and Section 8.3.7, “Counter Read.”)
D7
Reserved
D[6:4]
RTCSH[2:0]: RTC 10-second Counter Bits
These bits comprise a 3-bit BCD counter used to count tens of seconds.
The counter counts from 0 to 5 with a carry over of 1 from the 1-second counter. This counter is reset to
0 after 5 and outputs a carry over of 1 to the 1-minute counter.
D[3:0]
RTCSL[3:0]: RTC 1-second Counter Bits
These bits comprise a 4-bit BCD counter used to count units of seconds.
The counter counts from 0 to 9 synchronously with a 1-second signal derived from the 32.768-kHz
OSC1 clock. This counter is reset to 0 after 9 and outputs a carry over of 1 to the 10-second counter.
RTC Minute Register (RTC_MIN)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
RTC Minute
Register
(RTC_MIN)
0x300a05
(8 bits)
D7
–
reserved
–
–
–
0 when being read.
D6–4 RTCMIH[2:0] RTC 10-minute counter
0 to 5
X (
*
) R/W
D3–0 RTCMIL[3:0] RTC 1-minute counter
0 to 9
X (
*
) R/W
*
Software reset (RTCRST
→
1
→
0) does not affect the counter values. This register retains the value set before a software reset is
performed.
Note: Data should not be read from or written to the counters while 1 is being carried over. (See Section
8.3.5, “Counter Hold and Busy Flag,” and Section 8.3.7, “Counter Read.”)
D7
Reserved
D[6:4]
RTCMIH[2:0]: RTC 10-minute Counter Bits
These bits comprise a 3-bit BCD counter used to count tens of minutes.
The counter counts from 0 to 5 with a carry over of 1 from the 1-minute counter. This counter is reset to
0 after 5 and outputs a carry over of 1 to the 1-hour counter.
D[3:0]
RTCMIL[3:0]: RTC 1-minute Counter Bits
These bits comprise a 4-bit BCD counter used to count units of minutes.
The counter counts from 0 to 9 with a carry over of 1 from the 10-second counter. This counter is reset
to 0 after 9 and outputs a carry over of 1 to the 10-minute counter.