10 REAL-TIME CLOCK (RTCA)
10-6
Seiko Epson Corporation
S1C31D50/D51 TECHNICAL MANUAL
(Rev. 2.00)
RTCA provides interrupt enable bits corresponding to each interrupt flag. An interrupt request is sent to the CPU
core only when the interrupt flag, of which interrupt has been enabled by the interrupt enable bit, is set. For more
information on interrupt control, refer to the “Interrupt” chapter.
10.6 Control Registers
RTCA Control Register (Low Byte)
Register name
Bit
Bit name
Initial
Reset
R/W
Remarks
RTCACTLL
7
–
0
–
R
–
6
RTCBSY
0
H0
R
5
RTCHLD
0
H0
R/W Cleared by setting the
RTCACTLL.RTCRST bit to 1.
4
RTC24H
0
H0
R/W –
3
–
0
–
R
2
RTCADJ
0
H0
R/W Cleared by setting the
RTCACTLL.RTCRST bit to 1.
1
RTCRST
0
H0
R/W –
0
RTCRUN
0
H0
R/W
Bit 7
Reserved
Bit 6
RTCBSY
This bit indicates whether the counter is performing count-up operation or not.
1 (R):
In count-up operation
0 (R):
Idle (ready to rewrite real-time clock counter)
This bit goes 1 when performing 1-second count-up, +1 second correction, or 30-second correction. It
retains 1 for 1/256 second and then reverts to 0.
Bit 5
RTCHLD
This bit halts the count-up operation of the real-time clock counter.
1 (R/W): Halt real-time clock counter count-up operation
0 (R/W): Normal operation
Writing 1 to this bit halts the count-up operation of the real-time clock counter, this makes it possible
to read the counter value correctly without changing the counter. Write 0 to this bit to resume count-
up operation immediately after the counter has been read. Depending on these operation timings, the
+1 second correction may be executed after the count-up operation resumes. For more information on
the +1 second correction, refer to “Real-Time Clock Counter Operations.”
Note: When the RTCACTLH.RTCTRMBSY bit = 1, the RTCACTLL.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 RTCACTLL.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)