At the beginning of this month, we reviewed Embedded Lab’s (http://embedded-lab.com) tutorial for beginners on interfacing an LED dot matrix to PICMicro (http://www.embedds.com/interfacing-led-dot-matrix-display-to-pic/). It was a very good description of basic structure of LED dot matrix and how static characters are displayed on it. Embedded Lab has just posted a continuation of that and now explains how to scroll the characters on LED dot matrix display.
The LED matrix used has 8 rows and 16 columns. The sixteen columns are driven by two 8-bit serial-in-parallel-out shift registers (74HC595) whereas the eight rows are controlled through the decoded outputs from a decade counter (CD4017). This arrangement requires only 5 I/O pins of microcontrollers to drive the matrix of 128 LEDs, and therefore, a mid-range microcontroller can also be used (although, the author used PIC18F2550 microcontroller to demonstrate the technique).
The author explains in very detail how the individual display bit information are saved in a buffer and are continuously updated while scrolling the text message from right to left. The firmware was written in C and compiled with mikroC.