1 A compact display driver: the MAX7219
The MAX7219 is a compact, serial input/parallel output common-cathode display driver. Included on-chip there are a BCD code-B decoder, the multiplex scan circuitry, segment and digit drivers, and an 8×8 static RAM that stores each digit. Only one external resistor is required to set the segments current.
1.1 Common uses
This chip is often used to drive 7-segment display having up to 8 digits or up to 64 individual LEDs. It is not unusual find this chip in DIY kits to be mounted on a small PCBs like that used in this article (See Fig. 1).
This chip could be found in different packages and uses a non-standard SPI (Data is clocked even if CS remains high but is needed a low to high transition to complete communication.If you are not familiar with SPI communication read Meeting SPI). MAX7221 is similar to MAX7219 except for two parameters:
- MAX7221 segment drivers are slew-rate limited to reduce electromagnetic interference;
- its serial interface is fully SPI compatible.