1. Interfaces A practical approach. Lesson 2 I2C and SPI

2. Hardware description

3. PIC18F2580 board

4. PIC18F2580 board schematics

5. PIC18F2580 board connector

6. SPI Serial Peripheral Interface Bus
Devices communicate in master/slave mode where the master device initiates the data frame.

7. SPI Serial Peripheral Interface Bus 2
The SPI bus specifies four logic signals:
SCLK: Serial Clock (output from master);
MOSI; SIMO: Master Output, Slave Input (output from master);
MISO; SOMI: Master Input, Slave Output (output from slave);
SS: Slave Select (active low, output from master).

8. SPI Serial Peripheral Interface Bus 3
Advantages
Full duplex communication
Higher throughput than I²C or SMBus
Complete protocol flexibility for the bits transferred
Not limited to 8-bit words
Arbitrary choice of message size, content, and purpose
Extremely simple hardware interfacing
Typically lower power requirements than I²C or SMBus due to less circuitry (including pullups)
No arbitration or associated failure modes
Slaves use the master's clock, and don't need precision oscillators
Slaves don't need a unique address -- unlike I²C or GPIB or SCSI
Transceivers are not needed

9. SPI Serial Peripheral Interface Bus 3
Disadvantages
Requires more pins on IC packages than I²C, even in the "3-Wire" variant
No in-band addressing; out-of-band chip select signals are required on shared buses
No hardware flow control by the slave (but the master can delay the next clock edge to slow the transfer rate)
No hardware slave acknowledgment (the master could be "talking" to nothing and not know it)
Supports only one master device
No error-checking protocol is defined
Generally prone to noise spikes causing faulty communication
Without a formal standard, validating conformance is not possible
Only handles short distances compared to RS-232, RS-485, or CAN-bus

10. Hardware description SPI pic182550

11. MASTER SYNCHRONOUS SERIAL PORT (MSSP) SPI and I2C
• Serial Peripheral Interface (SPI)
• Inter-Integrated Circuit (I2C™)
- Full Master mode
- Slave mode (with general address call)
The I2C interface supports the following modes in hardware:
• Master mode
• Multi-Master mode
• Slave mode

12. SPI example with mcp28s08(1)

13. SPI example with mcp28s08(2)

14. Pic18f2580 SPI/I2C • Serial Data Out (SDO) – RC5/SDO
• Serial Data In (SDI) – RC4/SDI/SDA
• Serial Clock (SCK) – RC3//SCK/SCL
Additionally, a fourth pin may be used when in a Slave mode of operation:
• Slave Select (SS) – RA5/AN4/SS/

15. Inter-Intergrated circuit. I2C
Two-wire interface
Philips 1990’s
Opend Drain signals SDA SCL
+5V or 3.3 V
7 bits address -16 reserved = 112 nodes possible
10 kbits/s 100kbits/s 400 kbits/s 3.4Mbits/s

16. I2C Protocoll overheads Rp pull up for open drain. SDA SCL
Maximum bus capacitance 400 pF
Protocoll overheads
-slave address
-sometimes registeraddress
-ACK/NACK bits

17. I2C –bus protocol

18. I2C example MCP23008

19. I2C example MCP23008

20. I2C example MCP23008 init

21. I2C example MCP23008 data out

22. I2C example use of MCP23008