p10 led module doubts
From the first link on the web-page you linked to

http://digital-wizard.net/avr_projects/p10_led_display_panel_interface


  
  EN (Enable) is used for PWM brightness control of the entire panel. That means the MCU can control the brightness by feeding a pulse width modulated signal on this pin.
  A &amp; B are the multiplex select pins. They take binary input to select any one of the four multiplex rows.
  Shift clock, Store clock and Data are the normal shift register control pins. The shift register IC used is IC74HC595