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?
12/30/2018
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.
DUPLEX MEANS – BOTH DIRECTIONS AT ONCE
Master can receive from the slave at the same time as the master sends to the slave
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 --
12/30/2018
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 / or absence.
You could do “some” handshaking via software
12/30/2018
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)
12/30/2018
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
12/30/2018
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
12/30/2018
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
12/30/2018
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
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

10. Lab. 4 concept – Using an SPI interface to an LCD screen
SPI_TDBR Blackfin Processor SPI_RXBR
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 CJ7 / CJ8
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

11. Lab. 4 interface From Blackfin GET PIN ORDER CORRECT OR NOTHING WORKS
SPI lines (MOSI, CLK, PF5)
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

12. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
Lab Essentials (concept) of the Blackfin – LCD interface software
char HipHipArray[ ] = “Merry Christmas to all”;
SetUp_SPI_Interface(Baud_Rate); // Configure the SPI interface
// Activate SPI interrupts – register_handler for SPI_ISR, set SIC_IMASK
LCD_Display (WHICH_LCD, “CONTROL”, “CLEAR_SCREEN”);
UseFixedTimeASM(Enough_Time_For _LCD_To_Work_ClearScreen);
for (int count = 0; count < strlen(HipHipArray); count++) {
LCD_Display (WHICH_LCD, “DATA”, HipHipArray[count]); // Transmit the information we want from the array // one character at a time
UseFixedTimeASM(Enough_Time_For _LCD_To_Work_DataSent); }
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

13. LCD_Display (int, char*, char *); Concept – not actual implementation
LCD_Display (int lcd, char * type, char *operation) {
if (strcmp(type, “COMMAND”) == 0) { if (strcmp(operation, “CLEAR_SCREEN”) == 0) ClearScreen( );
if (strcmp(operation, “……..”) == 0) Do……..( ); }
if (strcmp(type, “DATA”) == 0) { if (strcmp(operation, “DISPLAY_TEMPERATURE”) == 0) DisplayTemperatureOnLCD( ); // Recursive call to LCD_Display
else WriteLetter(operation[0]); // First character
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

14. Example Commands Could we send commands like this?
char *LCDcommands[ ] = {                    "COMMAND", "INIT_LCD",                    "COMMAND", "CLEAR_SCREEN",                      "COMMAND", "MOVE_TO_LINE_1",                    "COMMAND", "CLEAR_LINE_1",                    "DATA", "4",     // This number is a 2 character string '4' and '\0'                    "DATA", "1",     // This number is a 2 character string '1' and '\0'                    "DATA", "5",     // This number is a 2 character string '5' and '\0'                      "COMMAND", "MOVE_TO_LINE_2",                    "COMMAND", "CLEAR_LINE_2",                   "DATA", "TEMPERATURE_DISPLAY"                    NULL, NULL};
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

15. 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?
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

16. What about the voltages that must go to the LCD?
Discussed those in the last lecture
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

17. SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
LCD Instruction set
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

18. 0 through 9, ( ) etc – all the same?
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

19. Is this a possible solution? Writing “Hello” to the LCD
ClearScreen( ); 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?
If you send CursorMove( ) and wait too long --
do you get two cursor moves?
If so – how do you stop that from happening?
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

20. Where does Blackfin fit in?
ClearScreen( );
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.
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

21. Blackfin transmits 16 bits with THIS format over the MOSI line
DB7, DB6, ………DB1, DB0
E – Enable / Strobe
1  0 – When this line goes from high to the low, then the command is send to (latched into) LCD
To make LCD respond to command 0x4F0 Then Blackfin must transmit 0x5F0 ( E High ) 0x4F0 ( E low ) 0x5F0 ( E high ) RS
1 – LCD data
0 – LCD instruction
R/W
1 – Read from LCD
0 – Write to LCD
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

22. Is this a possible solution? ClearScreenASM( )
Initialize the SPI interface in main( )
P0.L = lo(SPI_TDBR) – SPI transmit data buffer register
P0.H = hi(SPI_TDBR)
R0 = 0x0001; // LCD ClearScreen instruction
[P0] = R0;  Not correct – TDBR is 16-bit
R0 = some_value;
Call UseFixedTimeASM; // Wait for LCD to be done
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

23. Is this a POSSIBLE solution? WriteLetterASM(char whichletter)
P0.L = lo(SPI_TDBR) – SPI transmit data buffer register
P0.H = hi(SPI_TDBR)
R1 = 0x400; // Write data instruction // Need to make line RS = 1 for data
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
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

24. 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
Could be a problem if we “wait too long”. Perhaps multiple commands get sent to the LCD screen
We know the answer to the last question from the last lecture
Set the command with the EN bit high
Send the command with the EN bit low // Data goes into LCD on transition HI / LOW of EN-Bit
Send the command with the EN-bit high
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

25. Code MIGHT look like this then WriteLetterASM(char whichletter)
Save registers R7 and P5 properly to stack (how?)
P5.L = lo(SPI_TDBR)
P5.H = hi(SPI_TDBR)
R7 = R0; // which letter came in R0
R1 = 0x500; // Write data instruction // Need to make line RS = 1 for data and E = 1
R7 = R7 | R1;
W[P5] = R7; // Send data and control to LCD device
R0 = some_longer_value;
Call UseFixedTimeASM; // Wait for LCD to complete command
R1 = ~0x // Remove the E signal
R7 = R7 & R1
W[P5] = R7
Now add back the E-signal and store into W[P5] again
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

26. 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?
12/30/2018
SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada