Specifications

mikroElektronika | Free Online Book | PIC Microcontrollers | Appendix B: Examples
Here are a few important things that one should pay attention to when buying LED displays:
● Depending on whether anodes or cathodes are connected to the common pin, there are common anode displays and
common cathode displays. The figure above shows a common anode display. Looking at physical features, there is
no difference between these displays at all so it is recommended to check carefully prior installation which of them
is in use;
● For each microcontroller pin, there is a maximum current limitation it can receive or give. Because of this, if
several displays are connected to the microcontroller it is rec ommended to use so called Low current LEDs using
only 2mA for operation; and
● Display segments are usually marked with the letters from a to g, but there is no fast rule indicating to which micro
controller pins they should be connected. For this reason it is very important to check connecting prior to
commencing program writing or designing a device.
Displays connected to the microcontroller usually occupy a large number of valuable I/O pins, which can be a big problem
especially when it is needed to display multi-digital numbers. The problem is more than obvious if, for example, it is
needed to display two 6-digit numbers (a simple calculation shows that 96 output pins are needed in this case)! This
problem has a solution called MULTIPLEXING.
Here is how an optical illusion based on the same operating principle as a film camera is made. Only one digit at a time is
active, but they change their state so quickly that one gets impression that all digits of a number are active
simultaneously.
http://www.mikroe.com/en/books/picmcubook/appb/ (8 of 54)5/3/2009 11:36:02 AM