Datasheet

341
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
Figure 27-3. Boot Process Description
27.5.4 Store Program Memory Control and Status Register – SPMCSR
The Store Program Memory Control and Status Register contains the control bits needed to control 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 SPMEN 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 initiated, 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 – SIGRD: Signature Row Read
If this bit is written to one at the same time as SPMEN, the next LPM instruction within three clock cycles will
read a byte from the signature row into the destination register. see “Reading the Signature Row from Software”
HWBE
BOOTRST ?
Ext. Hardware
Conditions ?
Reset Vector = Application Reset Reset Vector =Boot Lhoader Reset
?
RESET
ALE/HWB
t
SHRH
t
HHRH
Bit 7 6 5 4 3 2 1 0
SPMIE RWWSB SIGRD RWWSRE BLBSET PGWRT PGERS SPMEN SPMCSR
Read/Write R/W R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0