Rainbow-electronics ATtiny2313 Uživatelský manuál stáhnout pdf (Strana 158)

158

ATtiny2313

2543A–AVR–08/03

EEPROM Write Prevents

Writing to SPMCSR

Note that an EEPROM write operation will block all software programming to Flash.

Reading the 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 (EEWE)

in the EECR Register and verifies that the bit is cleared before writing to the SPMCSR

Reading the Fuse and Lock

Bits from Software

It is possible to read both the Fuse and Lock bits from software. To read the Lock bits,

load the Z-pointer with 0x0001 and set the RFLB and SPMEN bits in SPMCSR. When

an LPM instruction is executed within three CPU cycles after the RFLB and SPMEN bits

are set in SPMCSR, the value of the Lock bits will be loaded in the destination register.

The RFLB and SPMEN bits will auto-clear upon completion of reading the Lock bits or if

no LPM instruction is executed within three CPU cycles or no SPM instruction is exe-

cuted within four CPU cycles. When RFLB and SPMEN are cleared, LPM will work as

described in the Instruction set Manual.

The algorithm for reading the Fuse Low byte is similar to the one described above for

reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and

set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within

three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the

Fuse Low byte (FLB) will be loaded in the destination register as shown below. Refer to

Table 69 on page 162 for a detailed description and mapping of the Fuse Low byte.

Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM

instruction is executed within three cycles after the RFLB and SPMEN bits are set in the

SPMCSR, the value of the Fuse High byte (FHB) will be loaded in the destination regis-

ter as shown below. Refer to Table XXX on page xxx for detailed description and

mapping of the Fuse High byte.

Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that

are unprogrammed, will be read as one.

Bit 76543210

Rd ––––––LB2LB1

Bit 76543210

Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0

Bit 76543210

Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0

1 2 ... 153 154 155 156 157 158 159 160 161 162 163 ... 210 211

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Rainbow-electronics ATtiny2313 Uživatelský manuál Strana 158