AT90S4414/8515
45
•
Bit 3 - CPOL: Clock Polarity
When this bit is set (one), SCK is high when idle. When CPOL is cleared (zero), SCK is low when idle. Refer to Figure 36
and Figure 37 for additional information.
•
Bit 2 - CPHA: Clock Phase
Refer to Figure 36 or Figure 37 for the functionality of this bit.
•
Bits 1,0 - SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a master. SPR1 and SPR0 have no effect on the slave. The
relationship between SCK and the Oscillator Clock frequency f
cl
is shown in the following table:
SPI Status Register - SPSR
•
Bit 7 - SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF bit is set (one) and an interrupt is generated if SPIE in SPCR is set (one) 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 when SPIF is set (one), then accessing the SPI Data Register (SPDR).
•
Bit 6 - WCOL: 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 (zero) by first reading the SPI Status Register when WCOL is set (one), and then accessing the SPI Data Register.
•
Bit 5..0 - Res: Reserved bits
These bits are reserved bits in the AT90S4414/8515 and will always read as zero.
The SPI interface on the AT90S4414/8515 is also used for program memory and EEPROM downloading or uploading. See
page 78 for serial programming and verification.
SPI Data Register - SPDR
The SPI Data Register is a read/write register used for data transfer between the register file and the SPI Shift register.
Writing to the register initiates data transmission. Reading the register causes the Shift Register Receive buffer to be read.
Table 17. Relationship Between SCK and the Oscillator Frequency
SPR1
SPR0
SCK Frequency
0
0
f
cl
/
4
0
1
f
cl
/
16
1
0
f
cl
/
64
1
1
f
cl
/
128
Bit
7
6
5
4
3
2
1
0
$0E ($2E)
SPIF
WCOL
-
-
-
-
-
-
SPSR
Read/Write
R
R
R
R
R
R
R
R
Initial value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
$0F ($2F)
MSB
LSB
SPDR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial value
x
x
x
x
x
x
x
x
Undefined