The first thing to get the MAX7219-driven LED matrix is ​​to connect and try to display the pattern. In addition to the GND and VCC, the MAX7219 requires only three additional pins to illuminate the matrix. Among them, DIN pin input data, CS (LOAD) pin control data input, CLK pin is used to distinguish each bit.
The entire write flow of MAX is that the CS pin is first set to 0, indicating that writes are allowed. Then, 16 bits are sequentially written from the upper order. Each bit is written in such a way that DIN is first set to the bit value to be written, and then CLK generates a falling edge (the rising edge in the figure, I don't know why there is a difference) is read. The last CS pin is set to indicate the end of the write.
The timing diagram is as follows:
Before running, an initialization is required, the behavior of which is to write a specific value to a few specific addresses. At least two addresses need to be written, the first one is 0x0b, and the 0x07 write indicates that all rows are scanned. The second is 0x0c, and writing 1 indicates entering the working mode.
Then each line on the dot matrix has its address. For example, the first line is 0x01 and the eighth line is 0x08. Each time an 8-bit binary number is written to the fixed line address, the pattern can be displayed on the specified line.
2. Raspberry Party GPIO Access - Virtual File System AccessLinux can access GPIO by accessing some files under sys/class/gpio and reading and writing these files.
! /bin/bash
# DIN, CS, GPIO port location of CLK
DIN=4
CS=3
CLK=2
# some file path
GPIO_BASE=/sys/class/gpio
GPIO_EXPORT=${GPIO_BASE}/export
GPIO_UNEXPORT=${GPIO_BASE}/unexport
BIN=(00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000)
# Generate the folder location of the specified GPIO pin
funcTIon GPIO(){
Echo ${GPIO_BASE}/gpio$1
}
# Export a pin to user mode
funcTIon GPIO_export(){
If [ -d `GPIO $1` ]; then
Echo GPIO pin $1 found in folder.
Else
Echo $1 》 ${GPIO_EXPORT}
Fi
}
# unexport a pin
funcTIon GPIO_unexport(){
If [ -d `GPIO $1` ]; then
Echo $1 》 ${GPIO_UNEXPORT}
Else
Echo GPIO pin $1 not found.
Fi
}
# Change the direction of a pin
funcTIon GPIO_direction(){
Echo $2 》 `GPIO $1`/direction
}
#Change the value of a pin
Function GPIO_set(){
Echo $2 》 `GPIO $1`/value
}
#Change the value of DIN
Function GPIO_DIN(){
GPIO_set $DIN $1
}
#Change the value of CS
Function GPIO_CS(){
GPIO_set $CS $1
}
#Change the value of CLK
Function GPIO_CLK(){
GPIO_set $CLK $1
}
# Send a byte value to MAX7219
Function Matrix_send_char(){
Local i=1
For ((i=1;i"=8;i++)); do
Chr=`expr substr $1 $i 1`
GPIO_DIN $chr
GPIO_CLK 1
GPIO_CLK 0
Done
}
# Send a complete signal to the MAX7219
Function Matrix_send_word(){
GPIO_CS 1
GPIO_CS 0
GPIO_CLK 0
Matrix_send_char $1
Matrix_send_char $2
GPIO_CS 1
}
# Initialize GPIO pins
Function GPIO_init(){
GPIO_export $DIN
GPIO_export $CS
GPIO_export $CLK
Sleep 2
GPIO_direction $DIN out
GPIO_direction $CS out
GPIO_direction $CLK out
}
# Clear GPIO pins
Function GPIO_clear(){
GPIO_unexport $DIN
GPIO_unexport $CS
GPIO_unexport $CLK
}
# Display data on the dot matrix
Function Matrix_render(){
Local i=1
For ((i=0;i"8;i++)); do
Echo $i $1
Matrix_send_word ${BIN[$i]} $1
Shift
Done
}
# Display using the data in the file
Function Matrix_render_file(){
Local tmp=(`cat $1`)
Matrix_render "${tmp[@]}"
}
# Use a pattern to clear the screen
Function Matrix_clear(){
Local STR=(
00000000
01100110
11111111
11111111
11111111
01111110
00111100
00011000
)
Matrix_render "${STR[@]}"
}
# Initialize the lattice
Function Matrix_init(){
#ç¼–ç 模å¼
Matrix_send_word 00001001 00000000
#亮
Matrix_send_word 00001010 00000011
#Scan number of digital tubes
Matrix_send_word 00001011 00000111
# Operating mode
Matrix_send_word 00001100 00000001
# Clear screen to display the default pattern after initialization
Matrix_clear
}
In the terminal:Source matrix.sh
GPIO_init
Matrix_init
The effect is as follows:
Pin insulator,Silicone rubber insulator,Composite insulator,Post insulator,Power fittings
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