Electronics- Matrix LCD Driver (MAX7219)denethor.wlu.ca/pc320/lectures/7219beam.pdfLED Matrix...

LED Matrix DisplaysMatrix Display Driver Chips

ElectronicsMatrix LCD Driver (MAX7219)

Terry Sturtevant

Wilfrid Laurier University

February 13, 2019

Terry Sturtevant Electronics Matrix LCD Driver (MAX7219)


LED Matrix Displays

Often LEDs will be arranged in a matrix, such as a severaldigit 7-segment or dot-matrix display.Rather than having a pin for each element, having pins foreach row and column reduces the total number needed.This requires strobing in order to work.



LED Matrix Displays

Often LEDs will be arranged in a matrix, such as a severaldigit 7-segment or dot-matrix display.

Rather than having a pin for each element, having pins foreach row and column reduces the total number needed.This requires strobing in order to work.



LED Matrix Displays

Often LEDs will be arranged in a matrix, such as a severaldigit 7-segment or dot-matrix display.Rather than having a pin for each element, having pins foreach row and column reduces the total number needed.

This requires strobing in order to work.



LED Matrix Displays

Often LEDs will be arranged in a matrix, such as a severaldigit 7-segment or dot-matrix display.Rather than having a pin for each element, having pins foreach row and column reduces the total number needed.This requires strobing in order to work.



LED matrix



LED 8 lighted



LED matrix operation

1 Set the bit for the first column HIGH, and all others LOW.2 Set the bits for each of the rows LOW where you want an

LED on, and set the others HIGH.3 Repeat for each column.




1 Set the bit for the first column HIGH, and all others LOW.

2 Set the bits for each of the rows LOW where you want anLED on, and set the others HIGH.

3 Repeat for each column.





LED on, and set the others HIGH.

3 Repeat for each column.





LED on, and set the others HIGH.3 Repeat for each column.



MAX7219 LED Display Driver ChipCurrent limiting

Matrix Display Driver Chips

This scenario use several digital signals, and requires constantrefreshing.It can be simplified with a driver chip which uses a serialinterface and refreshes automatically.The MAXIM MAX7219 is an example of this.





This scenario use several digital signals, and requires constantrefreshing.

It can be simplified with a driver chip which uses a serialinterface and refreshes automatically.The MAXIM MAX7219 is an example of this.





This scenario use several digital signals, and requires constantrefreshing.It can be simplified with a driver chip which uses a serialinterface and refreshes automatically.

The MAXIM MAX7219 is an example of this.





This scenario use several digital signals, and requires constantrefreshing.It can be simplified with a driver chip which uses a serialinterface and refreshes automatically.The MAXIM MAX7219 is an example of this.




MAX7219 LED Display Driver Chip

The MAXIM MAX7219 can handle up to 64 individual LEDs,in various arrangements.It uses an SPI interface to communicate, so it only requires 3signals.It is designed so that multiple MAX7219s can be cascaded tohandle much bigger displays.





The MAXIM MAX7219 can handle up to 64 individual LEDs,in various arrangements.

It uses an SPI interface to communicate, so it only requires 3signals.It is designed so that multiple MAX7219s can be cascaded tohandle much bigger displays.





The MAXIM MAX7219 can handle up to 64 individual LEDs,in various arrangements.It uses an SPI interface to communicate, so it only requires 3signals.

It is designed so that multiple MAX7219s can be cascaded tohandle much bigger displays.





The MAXIM MAX7219 can handle up to 64 individual LEDs,in various arrangements.It uses an SPI interface to communicate, so it only requires 3signals.It is designed so that multiple MAX7219s can be cascaded tohandle much bigger displays.




MAXX7219

The MAX7219 uses an SPI interface, and has outputs for 8 ‘rows’and 8 ‘columns’.




Basic wiring

For a dot matrix display, rows correspond to segments and columnscorrespond to digits.




Internal block diagram





8x8 SRAM stores bit values for the automatic refresh.





Multiplex scan circuitry handles the automatic refresh.





Intensity pulse width modulation controls brightness.





Code B ROM with bypass handles decode (or not) of individualdigits (or columns).




Data format

The address is 4 bits since there are 14 internal registers.




SPI details

Two byte SPI transfer keeps CS low between bytes.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.

There is one register for each digit.There are additional registers forshutdown,mode,intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.

There are additional registers forshutdown,mode,intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers for

shutdown,mode,intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,

mode,intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,

intensity,display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,intensity,

display test,and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,intensity,display test,

and scan limitThere is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,intensity,display test,and scan limit

There is also a no-op register.




Internal registers

The MAXIM MAX7219 has 14 internal registers.There is one register for each digit.There are additional registers forshutdown,mode,intensity,display test,and scan limitThere is also a no-op register.




Internal register configuration

Note digit register number has 1 added, since address zero is no-op.




Decode mode register

For dot matrix display you want no decode. For full digit displayuse decode for digits 0-7. (Set the bit for any digit(s) you wantdecoded.)




Code B format

As noted, D7 is for the decimal point. Decoding takes care ofdigits 0-9 plus a few letters.




Display test register

Display test mode turns on all segments. Normal operation uses8x8 SRAM.




Intensity register

Note 0 still gives 1/32 duty cycle.




Relationship between data bit and segment

With a dot matrix display, rows correspond to segments. (Columnscorrespond to digits.)




Scan limit register

Set the scan limit to the number of digits (or columns).




Shutdown register

Shutdown mode turns off display. Use normal mode otherwise.




Operation

To operate, place appropriate values in each of the registers.When all have been loaded, the display should be static untilvalues are changed.




Operation

To operate, place appropriate values in each of the registers.

When all have been loaded, the display should be static untilvalues are changed.




Operation

To operate, place appropriate values in each of the registers.When all have been loaded, the display should be static untilvalues are changed.




Current limiting

Current is limited by the Rset resistor.The value should be adjusted based on:the total number of digitsthe forward voltage of the LEDs




Current limiting

Current is limited by the Rset resistor.

The value should be adjusted based on:the total number of digitsthe forward voltage of the LEDs




Current limiting

Current is limited by the Rset resistor.The value should be adjusted based on:

the total number of digitsthe forward voltage of the LEDs




Current limiting

Current is limited by the Rset resistor.The value should be adjusted based on:the total number of digits

the forward voltage of the LEDs




Current limiting

Current is limited by the Rset resistor.The value should be adjusted based on:the total number of digitsthe forward voltage of the LEDs




Current limiting resistor

Note: Rset is in kΩ. Minimum value is 9.53kΩ for 40mA current.




Current and number of segments

Since corresponding segments for all digits are on simultaneously,current scales.




Questions

The MAX7219 is for common cathode displays.What would you have to do if you wanted to use commonanode displays?Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?What would happen if you did?What can you do if a display has more than 8 segments?




Questions

The MAX7219 is for common cathode displays.

What would you have to do if you wanted to use commonanode displays?Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?What would happen if you did?What can you do if a display has more than 8 segments?




Questions

The MAX7219 is for common cathode displays.What would you have to do if you wanted to use commonanode displays?

Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?What would happen if you did?What can you do if a display has more than 8 segments?




Questions

The MAX7219 is for common cathode displays.What would you have to do if you wanted to use commonanode displays?Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?

What would happen if you did?What can you do if a display has more than 8 segments?




Questions

The MAX7219 is for common cathode displays.What would you have to do if you wanted to use commonanode displays?Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?What would happen if you did?

What can you do if a display has more than 8 segments?




Questions

The MAX7219 is for common cathode displays.What would you have to do if you wanted to use commonanode displays?Since this is a 5V device, is there a problem connecting thesignals directly to Raspberry Pi GPIO pins?What would happen if you did?What can you do if a display has more than 8 segments?




Cascading devices

Connect all CS pins together.Connect Dout of each device to Din of the next one.To write to the Nth chip, send the desired 16-bit wordfollowed by N − 1 no-op codes.(i.e each write pushes the word to the next device in thechain.)




Cascading devices

Connect all CS pins together.

Connect Dout of each device to Din of the next one.To write to the Nth chip, send the desired 16-bit wordfollowed by N − 1 no-op codes.(i.e each write pushes the word to the next device in thechain.)




Cascading devices

Connect all CS pins together.Connect Dout of each device to Din of the next one.

To write to the Nth chip, send the desired 16-bit wordfollowed by N − 1 no-op codes.(i.e each write pushes the word to the next device in thechain.)




Cascading devices

Connect all CS pins together.Connect Dout of each device to Din of the next one.To write to the Nth chip, send the desired 16-bit wordfollowed by N − 1 no-op codes.

(i.e each write pushes the word to the next device in thechain.)




Cascading devices

Connect all CS pins together.Connect Dout of each device to Din of the next one.To write to the Nth chip, send the desired 16-bit wordfollowed by N − 1 no-op codes.(i.e each write pushes the word to the next device in thechain.)


LED Matrix DisplaysMatrix Display Driver ChipsMAX7219 LED Display Driver ChipCurrent limiting

Electronics- Matrix LCD Driver (MAX7219)denethor.wlu.ca/pc320/lectures/7219beam.pdfLED Matrix...

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