295
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
27.9 Register Description
27.9.1 SPMCSR – Store Program Memory Control and Status Register
The Store Program Memory Control and Status Register contains the control bits needed to con-
trol the Boot Loader operations.
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SELF-
PRGEN bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is initi-
ated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-Programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
• Bit 5 – Reserved
This bit is a reserved bit in the ATmega48A/PA/88A/PA/168A/PA/328/P and always read as
zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section is
blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, the
user software must wait until the programming is completed (SELFPRGEN will be cleared).
Then, if the RWWSRE bit is written to one at the same time as SELFPRGEN, the next SPM
instruction within four clock cycles re-enables the RWW section. The RWW section cannot be
re-enabled while the Flash is busy with a Page Erase or a Page Write (SELFPRGEN is set). If
the RWWSRE bit is written while the Flash is being loaded, the Flash load operation will abort
and the data loaded will be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four
clock cycles sets Boot Lock bits and Memory Lock bits, according to the data in R0. The data in
R1 and the address in the Z-pointer are ignored. The BLBSET bit will automatically be cleared
upon completion of the Lock bit set, or if no SPM instruction is executed within four clock cycles.
An LPM instruction within three cycles after BLBSET and SELFPRGEN are set in the SPMCSR
Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the
destination register. See ”Reading the Fuse and Lock Bits from Software” on page 287 for
details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SELFPRGEN, the next SPM instruction within four
clock cycles executes Page Write, with the data stored in the temporary buffer. The page
Bit 7 6 5 4 3 2 1 0
0x37 (0x57)
SPMIE RWWSB – RWWSRE BLBSET PGWRT PGERS SELFPRGEN SPMCSR
Read/Write R/W R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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