Fujitsu FR81S User Manual
CHAPTER 28: REAL-TIME CLOCK(RTC)
4. Registers
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER
: REAL-TIME CLOCK(RTC)
FUJITSU SEMICONDUCTOR CONFIDENTIAL
10
[bit7 to bit4] Reserved
These bits must always be written to "0".
[bit3] RUN : Operation state
RUN
State
0
Real-time clock module is stopped
1
Real-time clock module is running
[bit2] UPDT : Update
UPDT
State/Operation
Read
Write
0
Update completed
This does not affect the operations
1
Updating
The counter values of the Hour/ Minute/ Second counters are
updated to Day/ Hour/Minute/ Second register values
respectively.
Before writing "1" to the update bit (UPDT), set the value to be updated in the Day/ Hour/ Minute/ Second
registers.
Update for Day/ Hour/ Minute/ Second registers will be performed when reload occurs at the sub-second
counter ( 22-bit down counter).
When the counter value is updated, the UPDT bit will be cleared by hardware. However, when update is
completed at the same time as writing "1", the UPDT bit will not be cleared to "0".
[bit1] Reserved
This bit must always be written to "0".
[bit0] ST : Start
ST
Operation
0
Real-time clock module is stopped. All the counters are cleared.
1
Values set at Day/Hour/Minute/Second registers are loaded into
Day/Hour/Minute/Second counters, and the real-time clock starts to run.
Notes:
⋅
When writing "1" to the start bit (ST) from RTC stop state (ST=0) (RTC operation start), do not write
"1" to the update bit (UPDT) at the same time as the start bit.
(While ST=0, writing "1" as byte immediate value to the ST bit and the UPDT bit at the same time is
prohibited. )
⋅
To write "1" to the update bit (UPDT), do it while RTC is working (ST=1).
⋅
While the update bit (UPDT) is "1", writing "0" to the start bit (ST) (RTC stop) is prohibited.
MB91520 Series
MN705-00010-1v0-E
1049