ATMEGA8535 Datasheet, PDF (136/321 Pages) ATMEL Corporation – 8-bit Microcontrolle with 8K Bytes In-System Programmable Flash

Serial Peripheral
Interface – SPI
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer
between the ATmega8535 and peripheral devices or between several AVR devices.
The ATmega8535 SPI includes the following features:
• Full Duplex, Three-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 65. SPI Block Diagram⁽¹⁾
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Note: 1. Refer to Figure 1 on page 2, and Table 26 on page 60 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 66.
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
Registers, and the Master generates the required clock pulses on the SCK line to inter-
change 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.
When configured as a Master, the SPI interface has no automatic control of the SS line.
This must be handled by user software before communication can start. When this is
136 ATmega8535(L)
2502K–AVR–10/06