SPI Status Register 0
When addressing I/O Registers as data space using LD and ST instructions, the provided offset must be used. When using the I/O specific commands IN and OUT, the offset is reduced by 0x20, resulting in an I/O address offset within 0x00 - 0x3F.
| Bit7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| SPIF | WCOL | SPI2X | |||||
| AccessR | R | R/W | |||||
| Reset0 | 0 | 0 |
SPI Interrupt Flag
When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is in Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
Write Collision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set, and then accessing the SPI Data Register.
Double SPI Speed Bit
When this bit is written to logic one the SPI speed (SCK Frequency) will be doubled when the SPI is in Master mode (refer to Table 3). This means that the minimum SCK period will be two CPU clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4 or lower.
The SPI interface is also used for program memory and EEPROM downloading or uploading. See Serial Downloading for serial programming and verification.