spi compatible devices design and implementation details on the way to a valid spi-lcd interface...
TRANSCRIPT
SPI Compatible Devices
Design and implementation details on the way to a valid
SPI-LCD interface driver
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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?
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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What is SPI Serial Peripheral 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 -- http://www.totalphase.com/docs/articles/article03/• LCD information -- http://home.iae.nl/users/pouweha/lcd/lcd.shtml
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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)
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Concept of Master and Slave
Master• The component
that initiates the transfer
• The component that controls the transfer
Slave• The component
that responds to the transfer
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Master / Slave conceptSlave 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
FOR SAFETY – SELECT SIGNAL IS “ACTIVE LOW” NOT “ACTIVE HIGH”
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Master / Slave conceptMaster 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
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Master / Slave conceptSlave 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
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Lab. 4 concept – Using an SPI interface to an LCD screen
SPI_TDBR Blackfin Processor SPI_RXBR
LCD SCREEN CJ7 / CJ8 SWITCHES (LOGIC LAB)
SLAVE INPUT INTERFACE SLAVE OUTPUT INTERFACE
MOSI MISO
SLAVE SELECTPF5 used (PF0 to PF7)
DATACONTROL
SPICLOCK
LOADSlave toLCD
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Lab. 4 interfaceFrom Blackfin
SPI lines (MOSI, CLK, PF5)
GET PIN ORDERCORRECT
OR NOTHING WORKS
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Lab. 4 -- 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);
}
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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 }}
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Example CommandsCould 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};
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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?
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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What about the voltages that must go to the LCD?
Discussed those in the last lecture
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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LCD Instruction set
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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0 through 9, ( ) etc – all the same?
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Is this a possible solution?Writing “Hello” to the LCD
ClearScreen( );UseFixedTimeASM( );
CursorIncrease( ); UseFixedTimeASM( );DisplayOn( );
Use FixedTimeASM( );WriteLetter(‘H’); UseFixedTimeASM( );CursorMove( ); UseFixedTimeASM( );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?
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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 parallel interface
Possible solution -- Let us send out a ushort value 0x0001 from the Blackfin and arrange the wires from the interface to go to the LCD connections correctly• Top 8 bits of unsigned short value – LCD control• Bottom 8 bits of unsigned short value – LCD data
Page 10-17 -- 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.
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Blackfin transmits 16 bits with THIS format over the MOSI line
DB7, DB6, ………DB1, DB0
RS
1 – LCD data
0 – LCD instruction
R/W
1 – Read from LCD
0 – Write to LCD
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 0x4F0Then Blackfin must transmit 0x5F0 ( E High )0x4F0 ( E low )0x5F0 ( E high )
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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Is this a possible solution?Insert into ClearScreenASM( ) stub
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
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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 dataR0 = R0 | R1; // R0 contains 8-bit letterW[P0] = R0; // Send data and control
// to LCD device
R0 = some_longer_value;Call UseFixedTimeASM; // Wait for
// LCD
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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 R0R1 = 0x500; // Write data instruction
// Need to make line RS = 1 for data and E = 1R7 = 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 = ~0x100 // Remove the E signalR7 = R7 & R1W[P5] = R7
R0 = some_longer_value;Call UseFixedTimeASM; // Wait for LCD to complete command
Now add back the E-signal and store into W[P5] again
04/19/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada
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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?