![]() Decimal 4511 inputs The 4511 has three control inputs that allow you to: test the chip and display, by connecting the 'LT' (Lamp Test) input to 0V. The following table illustrates the point. This must be supplied the right-way round! Input D expects the most significant bit of the number, and input A the least significant bit. The inputs D, C, B and A, accept the binary number. The pin out for this chip is given in the diagram. The CMOS 4511 chip is a 7-segment decoder/driver, used with common-cathode displays. The 'driver' part of its name shows that it draws little current from the PICmicro to do so. This chip accepts a binary input, (well, binary-coded decimal to be more precise,) and converts it into the seven signals needed to control the display. An alternative is to use a decoder/driver chip to do some of the work. In some applications, that may not leave sufficient bits to operate other devices. However, that would take up seven bits of the PICmicro output port, one for each LED in the display. FACET by Lab-Volt 187ģ Decisions, Macros, and String Variables Microcontroller System Development Adding Drivers You can run a 7-segment display directly from the PICmicro chip. Normally, they are held at logic 0, but to light a segment, it is connected to logic 1. ![]() In the circuit, they are connected to the negative supply (0V) through a series resistor. In the common cathode format, all the cathodes are connected together internally. This can be done by connecting the display directly to the outputs of a PICmicro chip, or by using a decoder/driver integrated circuit. To make a segment light, the cathode of that LED is connected to logic 0. Normally, the cathodes of all the LEDs are held at logic 1. In use, they are then connected to the positive power supply through a series protective resistor. 186 FACET by Lab-VoltĢ Microcontroller System Development Decisions, Macros, and String Variables In the common anode format, all the anodes are connected together inside the 7-segment display package. The seven LEDs, (eight if you count the decimal point,) are interconnected in one of two ways, known as common-anode and common-cathode format. The pin arrangement of a typical 7-segment display is shown below. The next diagram illustrates how the number 3.57 can be displayed. EXERCISE DISCUSSION Adding Outputs - 7 Segment Displays These consist of seven LEDs arranged so that the numbers 0 to 9 can be displayed by lighting appropriate 'segments'. You will use Flowcode and the Microcontroller System Development FACET board to display a series of numbers. 1 Decisions, Macros, and String Variables Microcontroller System Development EXERCISE 2: The 7-Segment Display EXERCISE OBJECTIVE When you have completed this exercise, you will be able to describe the structure and function of a 7-Segment Display.
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