1 Introduction

When several alphanumeric display or pixel-oriented displays must be managed by a controller, the number of input-outputs (IOs) and the power needed for such controller can be a challenge. This takes 56 IOs to control 8-digits, 7-segment display if all the digits are active simultaneously. However, if a multiplexed display is implemented in the same size, just 15 IOs can accomplish the same job and, moreover, with less power.

In a Multiplexed Display, the LEDs in the segments or dots are organized in such way that the rows and the columns provide the data information (asserted high) and digit control (asserted low), respectively, as the Display Block diagram in Figure 1-1 shows.

Figure 1-1 Multiplexed Display Block Diagram

Each of the columns of a multiplexed display are driven one at time, the combination of high frequency and persistence of vision both together create the viewer’s illusion that the full display is active all the time. The activation sequence of of each of the rows is typically made more than 50 times for second, as is shown in the Figure 1-2.

Figure 1-2 Multiplexed Display Time Diagram

The TI programmable Logic Device (TPLD) can be configured to generate multiple block needed in the use case such the character generator, the CLK and synchronization signals and the multiplexer column selector as well. The LED-based monochrome Multiplexed Display in this example drives up to 16-columns 6-dots each, or this can be used for an 8-digits 7-segment display for alphanumeric messages or numbers, respectively. In the first case the design is using 3 TPLD and in the last case just 2 TPLD devices are needed. In both cases one of the TPLD is in charge of generate the data to be shown in the displays and the synchronization signals as well. The remaining TPLD devices are in charge of generating the columns multiplexer.