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μPD780948, μPD78F0948, μPD780949, μPD78F0949
Chapter 4 EEPROM
4.1 EEPROM Functions
The
μPD780949 Subseries contain on-chip 256 x 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 μPD780949 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 per 1 chip : 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).
(6) No code fetch is possible.
(7) No write operation is available in subsystem clock mode.
Note:
The EEPROM is only available in the μPD780949, μPD78F0949 and not in the
μPD780948, μPD78F0948.