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176
8246B–AVR–09/11
ATtiny2313A/4313
19.4.5
SPMCSR Can Not Be Written When EEPROM is Programmed
Note that an EEPROM write operation will block all software programming to Flash. Reading
fuses and lock bits from software will also be prevented during the EEPROM write operation. It is
recommended that the user checks the status bit (EEPE) in EECR and verifies that it is cleared
before writing to SPMCSR.
19.5
Preventing Flash Corruption
During periods of low V
CC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1.
Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating
voltage matches the detection level. If not, an external low V
CC reset protection circuit
can be used. If a reset occurs while a write operation is in progress, the write operation
will be completed provided that the power supply voltage is sufficient.
2.
Keep the AVR core in Power-down sleep mode during periods of low V
CC. This will pre-
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.
19.6
Programming Time for Flash when Using SPM
Flash access is timed using the internal, calibrated 8MHz oscillator. Typical Flash programming
Note:
1. Min and max programming times are per individual operation.
19.7
Register Description
19.7.1
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 Program memory operations.
Bits 7, 6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313A/4313 and always read as zero.
Table 19-2.
SPM Programming Time
Operation
Min
Max
SPM: Flash Page Erase, Flash Page Write, and lock bit write
3.7 ms
4.5 ms
Bit
76543210
–
RSIG
CTPB
RFLB
PGWRT
PGERS
SPMEN
SPMCSR
Read/Write
R
R/W
Initial Value
00000000