The MM74C911 display controller is an interface element with memory that drives a 4-digit, 8-segment LED display. The MM74C911 allows individual control of any segment in the 4-digit display. The number of segments per digit can be expanded without any external components. For example, two MM74C911's can be cascaded to drive a 16-seg- ment alpha-numeric display. The display controllers receive data information through 8 data lines a, b…DP, and digit information through 2 address inputs K1 and K2. The input data is written into the register selected by the address information when CHIP ENABLE, CE, and WRITE ENABLE, WE, are LOW and is latched when either CE or WE return HIGH. Data hold time is not required. A self-contained internal oscillator sequentially presents the stored data to high drive (100 mA typ.) 3-STATE output drivers which directly drive the LED display. The drivers are active when the control pin labeled SEGMENT OUTPUT ENABLE, SOE, is LOW and go into 3-STATE when SOE is HIGH. This feature allows for duty cycle brightness control, or for disabling the output drive for power conservation. The digit outputs directly drive the base of the digit transis- tor when the control pin labeled DIGIT INPUT OUTPUT, DIO, is LOW. When DIO is HIGH, the digit outputs are disabled and the digit inputs are available for external control of the digit segment decoders.
