Rainbow Electronics ATmega128L - Manual (Page 157)

157
ATmega128(L)
2467B–09/01
Serial Peripheral
Interface – SPI
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer
between the ATmega128 and peripheral devices or between several AVR devices. The
ATmega128 SPI includes the following features:
•
Full-duplex, 3-wire Synchronous Data Transfer
•
Master or Slave Operation
•
LSB First or MSB First Data Transfer
•
Seven Programmable Bit Rates
•
End of Transmission Interrupt Flag
•
Write Collision Flag Protection
•
Wake-up from Idle Mode
•
Double Speed (CK/2) Master SPI Mode
Figure 74. SPI Block Diagram
Note: Refer to Figure 1 on page 2, and Table 30 on page 69 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 75.
The system consists of two shift registers, and a Master clock generator. The SPI Mas-
ter initiates the communication cycle when pulling low the Slave Select SS pin of the
desired Slave. Master and Slave prepare the data to be sent in their respective shift reg-
isters, and the Master generates the required clock pulses on the SCK line to
interchange data. Data is always shifted from Master to Slave on the Master Out – Slave
In, MOSI, line, and from Slave to Master on the Master In – Slave Out, MISO, line. After
each data packet, the Master will synchronize the Slave by pulling high the Slave Select,
SS, line.
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128