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CHAPTER 4 EEPROM
4.1 EEPROM Functions
The
µ
PD780973 Subseries products contain on-chip 256
×
8-bit EEPROM (Electrically Erasable PROM) in addition
to internal high-speed RAM, as data memory.
EEPROM differs from ordinary RAM in that its contents are saved even after power is cut off. Moreover, unlike
EPROM, its contents can be erased electrically without using UV light. For this reason, it is suitable for applications
where the setting values of the odometer and trip meter on the dash board are saved, etc.
EEPROM can be manipulated with 8-bit memory manipulation instructions.
The EEPROM contained on-chip in the
µ
PD780973 Subseries has the following features.
(1) Written contents are saved even when the power is cut off.
(2) Can be manipulated with 8-bit memory manipulation instructions in the same way as ordinary RAM.
(3) Erasure and writing is performed in the time set with EWCS0 and EWCS1 (EEPROM write control register (EEWC)
bits 4 and 5) (see Figure 4-2). Therefore, the write time control software load is reduced. Moreover, during writing,
instructions other than instructions related to EEPROM writing and reading can also be executed.
• Rewrite frequency for all chips : 1,000,000 times
• Rewrite frequency per 1 byte : 100,000 times
Caution The values shown above are target values. These values are subject to change without notice,
so please contact your NEC sales representative for the latest value before designing.
(4) When write is completed, interrupt request signal (INTWE) is issued.
(5) The write enabled/disabled status can be checked with EWST (EEPROM write control register (EEWC) bit 1).
Содержание mPD780973 Series
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