SPI Eases Interfacing For 5-By-5 Dot-Matrix Display

March 21, 2013

The circuit interfaces a display that features four 5-by-5 dot-matrix characters by using the display’s serial peripheral interface and a programmable system on a chip (PSoC). The SPI reduces firmware overhead and enhances clock stability.

Girish Choudankar

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When discussing displays, seven-segment displays and LCDs are among the first that come to mind. Each type has its pros and cons. But generally, seven-segment displays cannot display letters, and LCDs tend to be bulky. Recently, I came across a four-character 5-by-5 dot-matrix, serial-input display (the SCDV5542 from Osram) that has several advantages.

The display can display alphanumeric characters and measures 10.16 by 19.91 mm (0.400 by 0.784 in.) with 3.12-mm (0.123-in.) characters. It has a serial peripheral interface (SPI) and allows high-speed data input. It features eight levels of dimming, an internal/external clock capability, and decoders, multiplexers, and an LED driver.

The device consists of a CMOS IC with control logic and drivers for the four 5-by-5 characters (Fig. 1). Each individual LED dot is addressable, so the user can create special characters. The device requires only four lines from a microcontroller. The IC accepts decoded serial data that is stored in internal RAM. Asynchronously, the RAM is read by the character multiplexer at the rate defined by the strobe.