21-16
MPC561/MPC563 Reference Manual
MOTOROLA
Programming Model
21.2.2
UC3F EEPROM Array Addressing
The UC3F array is divided into eight blocks, 64 Kbytes in size, which may be
independently erased. Two blocks are host to a 16-Kbyte small block.
Seventeen bits of address are used to decode locations in the UC3F array. The read control
logic in the UC3F EEPROM module decodes the upper 14 bits of that address to determine
if the desired data is currently stored in one of the two read page buffers. If the data is
already present in one of the two read page buffers, a read operation is not completed to the
UC3F array core, and 64 bits of data are transferred from the appropriate read page buffer
to the BIU. This type of array read access is an on-page read.
In the event that the read control logic determines that the desired data is not contained
within one of the read page buffers, a read access to the UC3F array core is completed and
32 bytes of data are transferred from the array core. Only the addressed 64 bits of data will
be transferred to the BIU. This type of array read access is an off-page read. The BIU
contains logic to implement the read page buffer update and replacement scheme to transfer
the 32 bytes of data into the appropriate read page buffer. If the read page update and
replacement scheme contains a random access mode that does not update the read page
buffers, the 32 bytes of data retrieved from the UC3F array core will not be transferred into
either read page buffer. The BIU is expected to contain page update logic for controlling
the updating of the read page buffers.
Write accesses to the UC3F array have no effect except during program and erase operation.
21.2.3
UC3F EEPROM Shadow Row
The UC3F EEPROM module contains a special shadow row that is used to hold reset
The shadow row is accessed by setting UC3FMCR[SIE] = 1 and performing normal array
accesses. Upon transitioning SIE (a 1-to-0 or 0-to-1 transition), the read page match decode
circuit is reset so that the next array access is an off-page access.
The shadow row contains 512 bytes which are addressed for read accesses using the low
order row and read page addresses.
The shadow row is implemented in the lowest numbered block of the array. In the case of
a UC3F array configuration which also has a small block in the lowest numbered block of
the array, the shadow row is contained in the small block. If SBEN[0] = 1 in this array
configuration, the shadow row is treated as part of small block 0. SBPROTECT[0] and
SBBLOCK[0] are used to control program and erase operation of the shadow row. If
SBEN[0] = 0 in this array configuration, the shadow row is treated as part of the host block.
The corresponding PROTECT and BLOCK bits are used to control program and erase
operation of the shadow row.