MIKROE Dot Matrix R Click is a display device Click board™ based on a four-digit dot matrix display module, labeled as HCMS-3906 from a company Avago (Broadcom Inc). The module holds four 5x7 dot matrices, with very closely spaced, bright red pixel elements. Characters are very clearly displayed as a result. Pixels emit a bright red color when lit, which makes the display readable in any condition. Each display can be directly interfaced with a microprocessor, thus eliminating the need for cumbersome interface components. The serial IC interface allows higher character count information displays with a minimum of data lines. The easy to read 5x7 pixel format allows the display of upper case, lower case, Katakana, and custom user-defined characters. The bright red display matrix has a wide viewing range, which makes it perfectly suited for low light situations.

Dot Matrix R Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.

Dot Matrix R Click is a high performance, easy to use dot matrix display driven by on-board CMOS IC. Each display can be directly interfaced with a microprocessor, thus eliminating the need for cumbersome interface components. The serial IC interface allows higher character count information displays with a minimum of data lines. The easy to read 5x7 pixel format allows the display of upper case, lower case, Katakana, and custom user-defined characters. These displays are stackable in the x- and y-directions, making them ideal for high character count displays. Typical applications include telecommunication equipment, portable data entry devices, computer peripherals, medical equipment, test equipment, business machines, avionics, industrial controls, etc.

Featured LED display HCMS-3906 consists of LEDs that are configured as 5x7 font characters driven in groups of 4 characters per IC. Each IC consists of a 160-bit shift register (the Dot Register), two 7-bit Control Words, and refresh circuitry. The Dot Register contents are mapped on a one-to-one basis to the display. Thus, an individual Dot Register bit uniquely controls a single LED. Reset initializes the Control Registers (sets all Control Register bits to logic low) and places the display in the sleep mode. The Dot Registers are not cleared upon power-on or by Reset. After power-on, the Dot Register contents are random; however, Reset will put the display in sleep mode, thereby blanking the LEDs. The Control Register and the Control Words are cleared to all zeros by Reset. To operate the display after being Reset, load the Dot Register with logic lows. Then load Control Word 0 with the desired brightness level and set the sleep mode bit to logic high.

The Dot Register holds the pattern to be displayed by the LEDs. First RS is brought low, then CE is brought low. Next, each successive rising CLK edge will shift in the data at the DIN pin. Loading a logic high will turn the corresponding LED on; a logic low turns the LED off. When all 160 bits have been loaded, CE is brought to logic high. When CLK is next brought to logic low, new data is latched into the display dot drivers. Loading data into the Dot Register takes place while the previous data is displayed and eliminates the need to blank the display while loading data.

In a 4-character display, the 160 bits are arranged as 20 columns by 8 rows. This array can be conceptualized as four 5x8 dot matrix character locations, but only 7 of the 8 rows have LEDs. The bottom row (row 0) is not used. Thus, latch location 0 is never displayed. Column 0 controls the left-most column. Data from Dot Latch locations 0-7 determine whether or not pixels in Column 0 are turned-on or turned-off. Therefore, the lower left pixel is turned on when a logic high is stored in Dot Latch location 1. Characters are loaded in serially, with the left-most character being loaded first and the rightmost character being loaded last. By loading one character at a time and latching the data before loading the next character, the figures will appear to scroll from right to left.

The Control Register allows software modification of the IC’s operation and consists of two independent 7-bit control words. Bit D7 in the shift register selects one of the two 7-bit control words. Control Word 0 performs pulse width modulation, pixel map, brightness control, peak pixel current brightness control, and sleep mode. Control Word 1 sets serial/simultaneous data out mode, and external oscillator prescaler. Each function is independent of the others.

This Click board™ can be supplied and interfaced with both 3.3V and 5V without the need for any external components. The onboard SMD jumper labeled as VCC SEL allows voltage selection for interfacing with both 3.3V and 5V microcontrollers.

• Interface: GPIO, SPI
• Compatibility: mikroBUS™
• Dimensions: 42.9 x 25.4mm
• Input Voltage: 3.3V or 5V

• Schematic
• HCMS-3906 Datasheet
• mikroSDK
• GitHub