HMS87C1808B Datasheet, PDF (79/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
20. POWER FAIL PROCESSOR
The HMS87C1X04B/08B/16B has an on-chip power fail detec-
tion circuitry to immunize against power noise. A configuration
register, PFDR, can enable (if clear/programmed) or disable (if
set) the Power-fail Detect circuitry. If V_DD falls below 2.1~3.0V
range for longer than 50 nS, the Power fail situation may reset
MCU according to PFS bit of PFDR.
As below PFDR register is not implemented on the in-circuit em-
ulator, user can not experiment with it. Therefore, after final de-
velopment of user program, this function may be experimented..
PFDR
Power Fail Detector Register
-
-
-
Reserved
-
PFDOPR PFDIS PFDM PFS
ADDRESS : EFH
RESET VALUE : ----0100
Power Fail Status
0 : Normal Operate
1 : This bit force to “1” when
Power fail was detected
Operation Mode
0 : System Clock Freeze during power fail
1 : MCU will be reset during power fail
Disable Flag
0 : Power fail detection enable
1 : Power fail detection disable
PFD Operation Disable Flag
0 : PFD operation enable
1 : PFD operation disable
Figure 20-1 Power Fail Detector Register
RESET VECTOR
PFS =1
YES
NO
RAM CLEAR
INITIALIZE RAM DATA
INITIALIZE ALL PORTS
INITIALIZE REGISTERS
Skip the
initial routine
FUNTION
EXECUTION
Figure 20-2 Example S/W of RESET by Power fail
SEP. 2004 Ver 1.03
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