Holtek HT66F20-1 Manual page 42

Programming Consideration
Care must be taken that data is not inadvertently written to the EEPROM. Protection can be
enhanced by ensuring that the Write Enable bit is normally cleared to zero when not writing. Also
the Bank Pointer could be normally cleared to zero as this would inhibit access to Bank 1 where
the EEPROM control register exist. Although certainly not necessary, consideration might be given
in the application program to the checking of the validity of new write data by a simple read back
process.
Programming Examples
Reading Data from the EEPROM – Polling Method
MOV A, EEPROM_ADRES
MOV EEA, A
MOV A, 040H
MOV MP1, A
MOV A, 01H
MOV BP, A
SET IAR1.1
SET IAR1.0
BACK:
SZ IAR1.0
JMP BACK
CLR IAR1
CLR BP
MOV A, EED
MOV READ_DATA, A
Writing Data from the EEPROM – Polling Method
MOV A, EEPROM_ADRES
MOV EEA, A
MOV A, EEPROM_DATA
MOV EED, A
MOV A, 040H
MOV MP1, A
MOV A, 01H
MOV BP, A
SET IAR1.3
SET IAR1.2
BACK:
SZ IAR1.2
JMP BACK
CLR IAR1
CLR BP
Rev. 1.40
HT66F20-1/HT66F30-1/HT68F20-1/HT68F30-1
; user defined address
; setup memory pointer MP1
; MP1 points to EEC register
; setup Bank Pointer
; set RDEN bit, enable read operations
; start Read Cycle - set RD bit
; check for read cycle end
; disable EEPROM read/write
; move read data to register
; user defined address
; user defined data
; setup memory pointer MP1
; MP1 points to EEC register
; setup Bank Pointer
; set WREN bit, enable write operations
; start Write Cycle - set WR bit
; check for write cycle end
; disable EEPROM read/write
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Flash MCU with EEPROM
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