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ST90E40G0 Ver la hoja de datos (PDF) - STMicroelectronics

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ST90E40G0 Datasheet PDF : 56 Pages
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EEPROM (Continued) EEPROM Programming Procedure
The programming of a byte of EEPROMmemory is
equivalent to writing a byte into a RAM location af-
ter verifying that EEBUSY bit is low. Instructions
operating on word data (16 bits) will not access the
The EEPROM ENABLE bit EEWEN must first be
set before writing to the EEPROM. When this bit is
low, attempts to write data to the EEPROM have
no affect, this prevents any spurious memory ac-
cesses from affecting the data in the EEPROM.
Termination of the write operation can be detected
by polling on the EEBUSY status bit, or by inter-
rupt, taking the interrupt vector from the External
Interrupt 4 channel. The selection of the interrupt is
made by EEPROM Interrupt enable bit EEIEN. It
should be noted that the Mask bit of External Inter-
rupt 4 should be set, and the Interrupt Pending bit
reset, before the setting of EEIEN to prevent un-
wanted interrupts. A delay (eg a nop instruction)
should also be included between the operationson
the mask and pending bits of External Interrupt 4.
If polling on EEBUSY is used, a delay of 6 INTCLK
clock cycles is necessary after the end of program-
ming, this can be a nop instruction or, normally,
therequired time to test the EEBUSY bit and to
branch to the next instruction will be sufficient.
While EEBUSY is active, any attempt to access the
EEPROM matrix will be aborted and the data read
will be invalid. EEBUSY is a read only bit and can-
not be reset by the user if active.
An erased bit of the EEPROM memory will read as
a logic “0”, while a programmed cell will be read as
a logic “1”. For applications requiring the highest
level of reliability, the Verify Mode, set by EEPROM
control register bit VRFY, allows the reading of the
EEPROM memory cells with a reduced gate volt-
age (typically 20%). If the EEPROM memory cell
has been correctly programmed, a logic “1” will be
read with the reduced voltage,otherwise a logic “0”
will be read. Parallel Programming Procedure
Parallel programming is a feature of the EEPROM
macrocell. One up to sixteen bytes of a same row
can be programmed at once.
The constraint is that each of the bytes occur in the
same ROW of the EEPROM memory (A4 constant,
A3-A0 variable). To operate this mode, the Parallel
Mode enable bit, PLLEN, must be set. The data
written is then latched into buffers (at the ad-
dresses specified, which may be non-sequential)
and then transferred to the EEPROM memory by
the setting of the PLLST bit of the control register.
Both PLLST and PLLEN are internally reset at the
end of the programming cycle. Any attempt to read
the EEPROM memory when PLLEN is set will give
invalid data. In the event that the data in the buffer
latches is not required to be written into the memory
by the setting of PLLST, the correct way to terminate
the operation is to reset PLLEN and to perform a
dummy read of theEEPROMmemory. This termina-
tion will clear all data present in the latches. EEPROM Programming Voltage
No external Vpp voltage is required, an internal
18Volt charge-pump gives the required energy by
a dedicated oscillator pumping at a typical fre-
quency of 5MHz, regardless of the external clock. EEPROM Programming Time
No timing routine is required to control the pro-
gramming time as dedicated circuitry takes care of
the EEPROM programming time (The typical pro-
gramming time is 6ms). EEPROM Interrupt Management
At the end of each write procedure the EEPROM
sends an interrupt request (if EEIEN bit is set). The
EEPROM shares its interrupt channel with the ex-
ternal interrupt source INT4, from which the priority
level is derived.
Care must be taken when EEIEN is reset. The as-
sociated external interrupt channel must be dis-
abled (by reseting bit 4 of EIMR, R244) along with
reseting the interrupt pending bit (bit 4 of EIPR,
R243) to prevent unwanted interrupts. A delay in-
struction (at least 1 nop instruction) must be in-
serted between these two operations
WARNING. The content of the EEPROM of the
ST9040 family after the out-going test at SGS-
THOMSON’s manufacturing location is not guar-
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