HCMS39xx Library

This library interfaces with Broadcom/Avago HCMS-39xx and HCMS-29xx series LED displays.

There are multiple displays in this series with various colors and display characters.

The library was specifically tested with a single HCMS-3964 display (4 character, 0.2", orange), but should work with other displays in either the 29xx or 39xx series. It should also work with multiple displays cascaded together.

Comparison With LedDisplay Library

This library provides similar functionality as the LedDisplay library. The following summarizes the main differences:

Functionality	HCMS39xx (this library)	LedDisplay library
Inherit from Print class	No	Yes
Flash size (bytes)	About 175 fewer bytes	About 175 more bytes
RAM size (bytes)	About 200 fewer bytes	About 200 more bytes
Cursors	Not supported	Supported
Scrolling	Not supported	Supported
BLANK pin	Supported	Not supported
SEL (oscillator select) pin	Supported	Not supported
Display sleep	Supported	Not supported
Display current control	Supported	Not supported
External oscillator prescale	Supported	Not supported
Font file character definitions	Standard plus 57 additional	ASCII 32 - 127 only
Simultaneous mode (see below)	Correct implementation	Ineffecient implementation

LedDisplay has a method to use simultaneous mode when writing control registers, but it serially writes all the chips to enable the mode when it uses it, thereby defeating the purpose of simultaneous mode.

Usage

Be sure to review the example sketches included with the library.

1. include the library header file:

   #include <HCMS39xx.h>

2. instantiate an HCMS39xx object:

   HCMS39xx myDisplay(uint8_t num_chars, uint8_t data_pin, uint8_t rs_pin, uint8_t clk_pin, 
                      uint8_t ce_pin, uint8_t blank_pin = NO_PIN, uint8_t osc_select_pin = NO_PIN);

   blank_pin and osc_select_pin have default values defined in the constructor, and therefore do not need to be included if they are not used (i.e., the are hardwired to specific logic levels instead of controlled by the microcontroller). It is also possible to use the enumeration HCMS39xx::NO_PIN if they are included in the constructor.

   The constructor sets the OSCILLATOR pin (if defined) to internal oscillator, the CE pin to HIGH (inactive), and the BLANK pin (if defined) to blank the display.

3. initialize the object (typically within setup()):

   myDisplay.begin();

   begin() initializes the LED hardware with default values:

   • Dot register is set to all 0s (all pixels off)
   • Control word 0 set to wakeup mode, default current (4.0 mA), default brightness (47%)
   • Control word 1 set to simultaneous mode and external prescaler turned off

4. Use the available library methods listed below to control the display.

Default State

The default state of the HCMS39xx object when instantiated is:

• Wakeup mode
• Display blanked
• Brightness level 12 (47 %)
• Display current level 4.0 mA
• Oscillator Select pin high (internal oscillator)
• External oscillator prescale divider 1
• Simultaneous mode enabled

Library Methods

  void print(const char* s);  // Print the characters pointed to by s to the display.
  void print(int j); // Prints the integer j. See below for more details, including other integer types supported.
  void printDirect(const uint8_t* d, uint8_t len); // Send the pixel data pointed to by d to the display. Direct pixel control of the display. 
  void clear();  // Clear the display (by writing all 0s to the dot register). [default]
  void displaySleep();  // Put the display into low power sleep mode. This turns off the pixel drivers and the internal oscillator. 
  void displayWakeup();  // Wake up the display. [default]
  void displayBlank();  // Blank the display using the blank pin. [default]
  void displayUnblank();  // Unblank the display using the blank pin -- need to unBlank() after begin().
  void setBrightness(uint8_t value); // Set display brightness level, where 0 <= value <= 15. [default is 12 (47%)]
  void setCurrent(DISPLAY_CURRENT value); // Set display current level. See header file for enumerated definitions for value. [default is 4.0 mA]
  void setExtOsc();  // Enable external oscillator with the oscillator select pin.
  void setIntOsc();  // Enable internal oscillator with the oscillator select pin. [default]
  void setExternalPrescaleDiv8();  // Set the external oscillator prescale divider to 8.
  void setExternalPrescaleNormal();  // Set the external oscillator prescale divider to 1. [default]
  void setSimultaneousMode();  // Enable simultaneous mode (only affects writes to control word registers). [default]
  void setSerialMode();  // Enable serial mode (only affects writes to control word registers).

print() is overloaded to support both string and integer parameters. The string version works as expected and prints the null-terminated string s to the display.

The integer version of print() is actually four separate functions to suport parameter types of int, unsigned int, long, and unsigned long integers. When using the integer version, if the number to be displayed has fewer digits than the display supports, then the number is left-padded with spaces. If the number is larger than can be represented on the display, then only the left-most digits will be shown. For example, when using a 4-digit display, 12345 will be displayed as 1234 and 8 will be displayed as <spc><spc><spc>8 (3 spaces and the numeral 8). For more complex display combinations, use snprintf() to format a string into a character buffer, and use print(const char* s) to display the formatted character buffer s.

Implementation Details

• The display is blanked when the object instance is initially created (if blank_pin is defined), so you need to use the displayUnblank() method before any characters will actually be visible on the display.
• The pixels are controlled bottom to top. The most significant bit (bit 7) of the dot data byte is unused. So to turn on the bottom pixel in a column, use a value of 0x40 with the printDirect() method. To turn on the top pixel, use 0x01.
• The pixel map for the 5x7 font included with this library is adapted from Broadcom Application Brief D-003 Table 1. A handful of pixel definitions were changed to make them look a little better than the ones defined in the table. In addition, several useful symbols were added at the end of the table with index values greater than 0x7F.
• The font5x7[] pixel map can be accessed from sketches if you #include "font5x7.h". It is therefore possible to create some effects like overlaying a strikethrough line across charactesr by reading the pixel data from font5x7[] and ORing it with 0x10 and using printDirect() to send the resulting pixels to the display.
• The pixel map in font5x7.h can be modified by adding character pixel maps to the bottom of the array. Note that you should also update the "last ASCII character" value at array position [1] if you add characters.
• It is also possible to save flash memory by decreasing the size of the font5x7[] array. In particular, 31 bytes can be saved by removing the symbols less than ASCII 0x20 (since those technically aren't ASCII characters anyway). Just be sure to update the "ASCII offset" value at array position [0].

Review the datasheet for other chip operation details.

Hardware Connections

When using the example sketches included in the library, connect the display as follows. See the device datasheet when configuring displays for other scenarios.

Four Digit Displays (HCMS-390x, HCMS-396x, HCMS-290x, and HCMS-296x)

Signal Name	Arduino	HCMS	Comment
DATA_OUT	NC	1	Leave unconnected unless cascading output to another HCMS
OSC	NC	2	Leave unconnected
V_LED	Vcc	3	See Note below
DATA_IN	6	4
RS	7	5
CLOCK	8	6
CE	9	7
BLANK	10	8
GND	GND	9
SEL	Vcc	10	See Note below
V_LOGIC	Vcc	11	See Note below
RESET	Vcc	12	See Note below

Eight Digit Displays (HCMS-391x, HCMS-397x, HCMS-291x, and HCMS-297x)

Signal Name	Arduino	HCMS	Comment
No Pin	NC	1	No physical pin, nothing to connect
No Pin	NC	2	No physical pin, nothing to connect
V_LED	Vcc	3	See Note below
No Pin	NC	4	No physical pin, nothing to connect
No Pin	NC	5	No physical pin, nothing to connect
No Pin	NC	6	No physical pin, nothing to connect
GND LED	GND	7
No Pin	NC	8	No physical pin, nothing to connect
No Pin	NC	9	No physical pin, nothing to connect
V_LED	Vcc	10	See Note below
No Pin	NC	11	No physical pin, nothing to connect
No Pin	NC	12	No physical pin, nothing to connect
No Pin	NC	13	No physical pin, nothing to connect
DATA_IN	6	14
RS	7	15
No Pin	NC	16	No physical pin, nothing to connect
CLOCK	8	17
CE	9	18
BLANK	10	19
GND LOGIC	GND	20
SEL	Vcc	21	See Note below
V_LOGIC	Vcc	22	See Note below
No Pin	NC	23	No physical pin, nothing to connect
RESET	Vcc	24	See Note below
OSC	NC	25	Leave unconnected
DATA_OUT	NC	26	Leave unconnected unless cascading output to another HCMS

Note

The 29xx series only works with 5 volt display and logic voltages per the datasheet. So connect all Vcc signals to 5 V.

The 39xx series works at either 3.3 or 5 volts. If using a 5 V Arduino (like the Uno), connect all Vcc signals to 5 V. If using a 3.3 V Arduino, connect all Vcc signals to 3.3 V.

References

• Broadcom HCMS-39xx series datasheet and HCMS-3964 product page
• Broadcom Application Note with ASCII font encoding data
• Broadcom HCMS-29xx series datasheet
• Arduino Playground description of the LedDisplay library

License

The software and other files in this repository are released under what is commonly called the MIT License. See the file LICENSE in this repository.