1. SPI Compatible Devices
Design and implementation details on the way to a valid SPI-LCD interface driver

2. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
To be tackled today
What is SPI?
What is the SPI “master slave” relationship?
How do you send commands from the Blackfin to a LCD device?
What commands are necessary to control the LCD device -- HD44780?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

3. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
What is SPI
Serial Parallel Interface – an industry standard
SPI is a serial communication bus developed by Motorola. It is a full-duplex protocol that functions on a master-slave paradigm that is ideally suited to data stream application.
Is essentially a 4 wire high speed system, with speeds up to many MHz
Blackfin (p10-8) has a register SPI_BAUD where they talk about transfer rates of 25 MHz.
Information is précised from
SPI information --
LCD information --
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

4. Advantages and drawbacks
SPI is a very simple communication protocol.
It does not have a specific high-level protocol which means that there is almost no overhead.
Data can be shifted at very high rates in full duplex mode
This makes it very simple and efficient in a single master single slave scenario.
The exchange itself has no pre-defined protocol. This makes it ideal for data-streaming applications.
Data can be transferred at high speed, often into the range of the tens of megaHertz.
The flipside is that there is no acknowledgment, no flow control, and the master may not even be aware of the slave's presence.
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

5. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Systems that use SPI
The question is of course, which peripheral types exist and which can be connected to the host processor. Peripheral types can be subdivided into the following categories:
Converters (ADC and DAC)
Memories (EEPROM and FLASH)
Real Time Clocks (RTC)
Sensors (temperature, pressure)
Others (signalmixer, potentiometer, LCD controller, UART, CAN controller, USB controller, amplifier)
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

6. Concept of Master and Slave
The component that initiates the transfer
The component that controls the transfer
Slave
The component that responds to the transfer
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

7. Master / Slave concept Slave Select (Chip Select)
Master sends out active low chip select signal SS1, then slave 1 responds
Master sends out active low chip select signal SS2, then slave 2 responds
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

8. Master / Slave concept Master to Slave data movement
Master sends out information to slave on MOSI wire
Slave receives information from the master on MOSI wire
Information (bits) is clocked by SCLK signal.
1-bit, 1 clock tick
MOSI --MASTER OUT – SLAVE IN
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

9. Master / Slave concept Slave to Master data movement
Master receives information from slave on MISO wire
Slave sends information to the master on MISO wire
Information (bits) is clocked by SCLK signal.
1-bit, 1 clock tick
MISO --MASTER IN – SLAVE OUT
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

10. Lab. 5 concept – Using an SPI interface to an LCD screen
Blackfin Processor
SLAVE SELECT PF5 used (PF0 to PF7)
SPI CLOCK
MOSI
MISO
SLAVE OUTPUT INTERFACE
SLAVE INPUT INTERFACE
LOAD Slave to LCD
DATA
SWITCHES (LOGIC LAB)
CONTROL
LCD SCREEN
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

11. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Lab. 5 interface
From Blackfin
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

12. Lab. 5 Essentials of the Blackfin – LCD interface software
char HipHipArray[ ] = “Merry Christmas to all”;
SetUp_SPI_Interface(Baud_Rate); // Configure the SPI interface
LCD (CONTROL_REQUEST, CLEAR_SCREEN);
for (int count = 0; count < strlen(HipHipArray); count++) {
LCD (DATA_REQUEST, HipHipArray[count]); // Transmit the information we want
UseFixedTimeASM(Enough_Time_For _LCD_To_Work); }
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

13. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
What we need to know?
How do we make the LCD screen respond to control requests?
Clear screen, move cursor, next line etc
How do we make the LCD screen respond to data requests?
Display letter a, b, C, 1, 2, (, ?, h etc
How do we get Blackfin SPI interface to send the LCD screen those commands?
How to we initialize the Blackfin SPI interface so all the above things work?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

14. What about the voltages that must go to the LCD?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

15. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
LCD Instruction set
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

16. Details of what is needed
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

17. Data to send a character
Complicated or not?
To cause “A” to appear on LCD screen need bit pattern = 0x41 sent to LCD data pins
Also send the necessary LCD control signals
How do the letter bit patterns for the LCD data patterns relate to ASCII bit patterns?
standard format used to store characters in a C++ character array?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

18. A to Z, a to z Coding exactly the same?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

19. 0 through 9, ( ) etc – all the same?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

20. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Some commands
LCD COMMANDS RS
R/W
DATA DB7 to DB0
ClearScreen( )
0x01
CursorIncrease( )
0x05
CursorMove( )
0x10
DisplayOn( )
0x0B
WriteLetter(value) 1
value
WriteLetter(‘a’)
0x61 (ascii ‘a’)
WriteLetter(‘A’)
0x41 (ascii ‘A’)
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

21. Is this a possible solution? Writing “Hello” to the LCD
ClearDisplay( ); UseFixedTimeASM( );
CursorIncrease( );
UseFixedTimeASM( );
DisplayOn( ); Use FixedTimeASM( );
WriteLetter(‘H’);
CursorMove( );
WriteLetter(‘e’);
etc.
General concept is there,
The exact details will have to
wait a while
QUESTION! What happens if you send a CursorMove( ) command and wait too long?
Do you get two cursor moves?
If so – how do you stop that from happening?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

22. Where does Blackfin fit in?
ClearDisplay( );
This means that the following bits must be sent RS = 0, R/W = 0, DB7=DB6=DB5….DB1 = 0, DB0 = 1; from Blackfin SPI interface to LCD
Possible solution -- Let us send out the ushort value 0x0001 from the Blackfin and arrange the wires from the interface to go to the LCD connections correctly
Top 8 bits of ushort value – LCD control
Bottom 8 bits of ushort value – LCD data
Page SPI Transmit Data Buffer Register SPI_TDBR – 16-bit read/write register.
Data loaded into this data register is automatically transmitted over the SPI interface if the SPI interface is enabled for transmission.
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

23. Is this a possible solution? ClearDisplayASM( )
Initialize the SPI interface in main( )
P0  SPI_TDBR – SPI transmit data buffer register
R0 = 0x0001; // LCD instruction
[P0] = R0;  Not correct – TDBR is 16-bit
R0 = some_value;
Call UseFixedTimeASM;
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

24. Is this a better solution? WriteLetterASM(char whichletter)
P0  SPI_TDBR – SPI transmit data buffer register
R1 = 0x200; // Write data instruction
R0 = R0 | R1; // R0 contains 8-bit letter
W[P0] = R0; // Send data and control // to LCD device
R0 = some_longer_value;
Call UseFixedTimeASM; // Wait for // LCD
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

25. Is this a better version? WriteLetterASM(char whichletter)
P0  SPI_TDBR – SPI transmit data buffer register
R1 = 0x200; // Write data instruction
R0 = R0 | R1;
W[P0] = R0;
R0 = some_longer_value;
Call UseFixedTimeASM;
Call CursorMove; // Get ready for next
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

26. Questions still unanswered
How do we configure the SPI interface inside the Blackfin?
How do we activate the chip-select line – PF5?
Does activating the PF5 line as SPI output control mean we have to change all the SetupPF8to11ASM( ) and other routines?
When do we activate the chip-select line, and how long for?
How do we know when LCD is ready for next character – do we poll a bit and wait till ready, or can it be done in the background?
How do we stop multiple commands from being accidentally sent to LCD? -- cursor move etc
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

27. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Tackled today
What is SPI?
What is the SPI “master slave” relationship?
How do you send commands from the Blackfin to a LCD device?
What commands are necessary to control the LCD device -- HD44780?
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

28. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Information taken from Analog Devices On-line Manuals with permission
Information furnished by Analog Devices is believed to be accurate and reliable. However, Analog Devices assumes no responsibility for its use or for any infringement of any patent other rights of any third party which may result from its use. No license is granted by implication or otherwise under any patent or patent right of Analog Devices. Copyright  Analog Devices, Inc. All rights reserved.
11/28/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada