On EEPROM write operations (after setting the
STORE bit) the values of the CONFIGURATION
REGISTER and BASE REGISTER are written in
the EEPROM locations defined by the IOS2-0
pins.
PURPOSE REGISTER is written at the
EEPROM word address defined by the
POINTER REGISTER 6 least significant bits.
RELOAD and STORE are set by the user to
initiate read and write operations respectively.
Polling the value until read low is used to
The three least significant bits of the CONTROL
REGISTER (EEPROM SELECT, RELOAD and
STORE) are used to control the EEPROM.
Their values are not stored nor loaded from the
EEPROM.
determine completion.
When an EEPROM
access is in progress the STORE and RELOAD
bits of CTR will readback as both bits high. No
other bits of FEAST can be read or written until
the EEPROM operation completes and both bits
are clear. This mechanism is also valid for
reset initiated reloads.
b) GENERAL
PURPOSE
REGISTER
-
EEPROM SELECT bit = 1
On EEPROM read operations (after setting
RELOAD high) the EEPROM word address
defined by the POINTER REGISTER 6 least
significant bits is read into the GENERAL
PURPOSE REGISTER.
Note: If no EEPROM is connected to the
LAN91C900, for example for some embedded
applications, the ENEEP pin should be
grounded and no accesses to the EEPROM will
be attempted. Configuration, Base, and
Individual Address assume their default values
upon hardware reset and the CPU is responsible
for programming them for their final value.
On EEPROM write operations (after setting the
STORE bit) the value of the GENERAL
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