Saturday, 26 October 2013

About MAX7219 LED Display Dot-matrix Display Driver - Data Format - Register Map - Programming


                The MAX7219 chip from maxim is a powerful serial input/output common-cathode display driver that interfaces microcontroller to 7-segment numeric LED displays of up to 8 digits and a 8x8 dot-matrix displays. The pindiagram of MAX7219 is (for MAX7221, pin 12 is CS_bar)

MAX7219
Typical application circuit is


Many MAX7219 can be cascaded serially through DOUT pin of one IC to DIN of the another, but with common clock and load connections. 

        It needs only 3 wires to interface with the microcontroller or microprocessor namely, CLK, LOAD and DIN. It has a build-in BCD (binary code decimal) decoder and a brightness control. It is easy to enable or disable the BCD decoder through the registers. Although the main function is to drive the 8-Digits seven segment LED display but because it also capable to drive an individual LED segment i.e. segment A to segment G and DP (decimal point), by disabling the decoder.

         The MAX7219 chip has 16-bit registers divided into two ADDRESS and DATA each of 8 bit size. The data format for programming is
at the negative edge of CLK, the DIN appears at DOUT for cascading

                In order to send a command to the MAX7219 chip, first we need send the 8-bits address and next we send the 8-bits data. It uses D8-D11 as address to map 14 registers. The register map is //               

           //Max7219 Command registers Address
               DECODE         0x09      // Decode mode register Address
               INTENSITY     0x0A      // Intensity register Address
               SCAN_LIMIT   0x0B      // Scan limit register Address
               SHUTDOWN   0x0C      // Shutdown register Address
               DISPLAY_TEST  0x0F     // Display test" register Address
               NOP  0x00
               D0  0x01
               D1  0x02
               D2  0x03
               D3  0x04
               D4  0x05
               D5  0x06
               D6  0 x07
               D7  0x08

          The data byte should be proceeded by the address byte.
       The segment current is set by an external resistor (Rset) connected to pin 18 and VCC. The intensity can be controlled by software using Intensity register, setting values 1 (min) to 15 (max).

          The Shutdown mode turns off all segment drives if its data is 0x00 and normal op if 0x01.

          The Display test mode turns on all segment drives if its data is 0x01 and normal op if 0x00.

        The Decode register is used to enable BCD decoder for the digits. the values are NONE=0x00,  D0=0x01,  D0-D3=0x0F,  D0-D7=0xFF

        The Scan limit register is used to set the number of used digits. 

      The same principle is also apply to other important MAX7219 chip commands such as activate from the shutdown mode (normal operation), use BCD decode (code B) mode, scanning limit (scanning digit 0 to 7), and adjusting the seven segment LED digit intensity please refer to the Maxim MAX7219 datasheet for the complete explanation.


          Comming soon: Interfacing MAX7219 with AVR for 7seg LEDs & later 8x8 dot matrix displays... Stay Tuned. Dont miss it.


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