The MAX6954 is a universal display driver that can control multiple discrete, 7-segment, 14-segment, or 16-segment LED displays via a serial port. This application note describes typical applications and configurations for driving 8-bit monochrome, 14-segment LED displays.
For more information about MAX6954, please refer to the MAX6954 data sheet.
The application notes "Quick Start: Using the MAX6954 to Drive a 7-Segment LED Display" and "Quick Start: Using the MAX6954 to Drive a 16-Segment LED Display" are similar to this article and describe how to configure the MAX6954 to drive 7- and 16-segment displays, respectively.
Click to enlarge Figure 1. MAX6954 drives a 14-segment display circuit
Table 1. Connection table with eight-digit 14-segment display
| DIGIT | O0 | O1 | O2 | O3 | O4 | O5 | O6 | O7 | O8 | O9 | O10 | O11 | O12 | O13 | O14 | O15 | O16 | O17 | O18 |
| 0 | CCO | - | a | - | b | c | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 1 | - | CC1 | a | - | b | c | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 2 | a | - | CC2 | - | b | c | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 3 | a | - | - | CC3 | b | c | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 4 | a | - | b | c | CC4 | - | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 5 | a | - | b | c | - | CC5 | d | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 6 | a | - | b | c | d | - | CC6 | - | e | f | g1 | g2 | h | i | j | k | l | m | dp |
| 7 | a | - | b | c | d | - | - | CC7 | e | f | g1 | g2 | h | i | j | k | l | m | dp |
Figure 2. Segment identification of the 14-segment display
Figure 3. 14-segment display font
A common application of the MAX6954 is to drive up to 8-bit 14-segment monochrome LEDs. This application note guides the user how to connect the MAX6954 to a 14-segment display, and how to configure its internal registers to control the display of 104 characters in a built-in font.
The MAX6954 uses a multiplexing technique that alternates the polarity of the driver port to reduce the number of pins. This is different from the standard LED multiplexing connection used separately for the cathode and anode pins of the driver. Application note 1880 discusses this technique. Table 1 is the connection table between MAX6954 and 14-segment display. This table is compatible with the MAX6954 multiplexing configuration and its 104-character built-in font. The letters in Table 1 correspond to the segment identifiers in Figure 2. Figure 1 is a schematic diagram of the MAX6954 driving an eight-bit 14-segment display.
After the MAX6954 is connected to the 14-segment display, the display test mode can be used to check the correctness of the connection. The display test mode is not affected by the control and data registers, and lights all segments of the display, but does not change any register contents. Write 0x01 to register 0x07 to start the display test mode. In the test mode, if there is an unlit segment on the display, the connection is incorrect. Write 0x00 to register 0x07 to exit display test mode.
After completing the connection check, you need to set the MAX6954 register value as required to drive the 14-segment display. Table 2 includes the power-on initial values ​​of some important registers of MAX6954. The MAX6954 is in power-down mode when it is first powered on. Every bit of display is blanked, and the number of scanning digits is set to the maximum, that is, eight digits. The MAX6954 can be set to drive the 14-segment display by writing 0xFF to register 0x0C. The default value of the decoding mode register (0x01) is suitable for 14-segment display.
Table 2. MAX6954 register power-on initial state
| REGISTER | POWER-UP CONDITION | ADDRESS (HEX) | REGISTER DATA | |||||||
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | |||
| Decode Mode | Font map enabled | 0x01 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| Global Intensity | 1/16 (minimum intensity) | 0x02 | X | X | X | X | 0 | 0 | 0 | 0 |
| Scan Limit | Display eight digits: 0, 1, 2, 3, 4, 5, 6, 7 | 0x03 | X | X | X | X | X | 1 | 1 | 1 |
| Control Register | Shutdown enabled, blink disabled, blink speed is slow | 0x04 | 0 | 0 | X | X | 0 | 0 | 0 | 0 |
| Display Test | Normal operaTIon (display test disabled) | 0x07 | X | X | X | X | X | X | X | 0 |
| Digit Type | Digits 0 through 7 are 16 segment digits | 0x0C | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Intensity10 | 1/16 (min on), digits 1 and 0 | 0x10 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Intensity32 | 1/16 (min on), digits 3 and 2 | 0x11 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Intensity54 | 1/16 (min on), digits 5 and 4 | 0x12 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Intensity76 | 1/16 (min on), digits 7 and 6 | 0x13 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Digit 0 | Blank digit, both planes | 0x60 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 1 | Blank digit, both planes | 0x61 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 2 | Blank digit, both planes | 0x62 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 3 | Blank digit, both planes | 0x63 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 4 | Blank digit, both planes | 0x64 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 5 | Blank digit, both planes | 0x65 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 6 | Blank digit, both planes | 0x66 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Digit 7 | Blank digit, both planes | 0x67 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
The configuration register (0x01) is used to set the entry and exit of shutdown mode, control the flashing function, globally clear the data of each bit, and select whether to control the brightness of each bit globally or individually. The configuration register contains 7 bits (see Table 3).
The S bit is used to select the shutdown mode or normal operation mode (read / write). Bit B is used to select the blinking rate (read / write). The E bit is used to globally enable or disable the flashing function (read / write). The T bit is used to reset the flashing sequence (this data is not stored-transient bit). The R bit is used to globally clear the P0 and P1 two-level registers corresponding to all display bits (this data is not stored-transient bit). The I bit is used to select whether the brightness of each bit is controlled globally or individually (read / write). The P bit is used to return to the current flash timing phase (read-only-writing to this bit will be ignored).
Start the display driver by writing 0x01 to register 0x04, and at the same time set the working mode to global brightness control and prohibit flashing. The internal oscillator starts when the MAX6954 exits shutdown mode, and the oscillator output pin is OSC_OUT. Note that when the power-on state of the data control registers 0x60 to 0x67 is 0x20 or no segment is lit, the 14-segment display remains blanked (see Table 2 and Figure 3).
Table 3. Configuration register format
| CONFIGURATION REGISTER DATA BIT | DATA BIT LABEL | STATE | FUNCTION |
| D7 | P | 0 | P1 Blink Phase |
| 1 | P0 Blink Phase | ||
| D6 | I | 0 | Intensity for all digits is controlled by one setting in the Global Intensity Register |
| 1 | Intensity for digits is controlled by the individual settings in the Intensity10 through Intensity76 registers. | ||
| D5 | R | 0 | Digit data for both planes P0 and P1 are unaffected |
| 1 | Digit data for both planes P0 and P1 are cleared on the rising edge of / CS \ | ||
| D4 | T | 0 | Blink timing counters are unaffected. |
| 1 | Blink timing counters are reset on the rising edge of / CS \. | ||
| D3 | E | 0 | Blink function disabled |
| 1 | Blink function enabled | ||
| D2 | B | 0 | Slow Blinking. Segments blink on for 1s, off for 1s with fOSC = 4MHz. |
| 1 | Fast Blinking. Segments blink on for 0.5s, off for 0.5s with fOSC = 4MHz. | ||
| D1 | X | X | Don't care |
| D0 | S | 0 | Shutdown |
| 1 | Normal Operation |
Table 4. Display data combination configuration examples
| DIGIT TYPE REGISTER SETTING | ADDRESS CODE (HEX) | REGISTER DATA | |||||||
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | ||
| Digits 7-0 are 14-segment digits | 0x0C | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
The MAX6954 has a built-in 104-character ASCII font for 14-segment displays. The characters are standard ASCII fonts plus these commonly used symbols. The 104 characters are represented by 7 digits, and the 8th digit is used to select whether to light the decimal point (DP) (see Table 5). The data register has two levels, P0 and P1. Each display bit is represented by 2 bytes in the memory, one byte is at P0 and the other is at P1 (see Table 8). The data register is a mapped address mode, so each bit of data can be updated in P0 (registers 0x20 to 0x27) or P1 (registers 0x40 to 0x47), and it can also be updated in two stages (registers 0x60 to 0x67). The data in the data register does not directly control the display of each segment in the 14 (original error is 16) segment display. Instead, it is used to address a character generator that stores 14 segments of font data (see Figure 3). The lower 7 bits of the register data (D6 to D0) are used to select characters from the font. The highest digit (D7) controls the decimal point (DP) display; set to 1 to display DP, and set to 0 to not display DP.
Table 5. Data register format
| MODE | ADDRESS CODE (HEX) | REGISTER DATA | |||||||
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | ||
| 14-segment mode, writing digit data to use font map data with decimal place unlit | 0x20 to 0x27 0x40 to 0x47 0x60 to 0x67 | 0 | Bits D6 to D0 select font character 0 to 127 | ||||||
| 14-segment mode, writing digit data to use font map data with decimal place lit | 0x20 to 0x27 0x40 to 0x47 0x60 to 0x67 | 1 | Bits D6 to D0 select font character 0 to 127 | ||||||
If the flash function is disabled by the configuration register flash enable bit E (see Table 3), the data in the data register in P0 is used as the display multiplex. The data in the data register in P1 is not used. If the blinking function is enabled, the data multiplexing display in P0 and P1 is used alternately. The data in P0 and P1 are applied to different phases of the blinking clock alternately changing, thereby multiplexing the LED display to achieve the blinking function.
The following is an example of using the MAX6954 driver to display eight characters, "MAXIM-IC". Set the configuration register to disable the flashing function, so that you can control data bits 0 to 7 by writing data to registers 0x20 to 0x27. Use the font diagram in Figure 3 to get the code corresponding to each character.
Table 6. Examples of MAXIM-IC
| REGISTER ADDRESS (HEX) | DIGIT | CHARACTER | FONT MAP EQUIVALENT CODE | |
| DECIMAL | HEX | |||
| 0x20 | 0 | M | 0100 1101 | 0x4D |
| 0x21 | 1 | A | 0100 0001 | 0x41 |
| 0x22 | 2 | X | 0101 1000 | 0x58 |
| 0x23 | 3 | I | 0100 1001 | 0x49 |
| 0x24 | 4 | M | 0100 1101 | 0x4D |
| 0x25 | 5 | - | 0010 1101 | 0x2D |
| 0x26 | 6 | I | 0100 1001 | 0x49 |
| 0x27 | 7 | C | 0100 0011 | 0x43 |
Adjust the display brightness by writing data to register 0x02 (Global Brightness Control Register). The brightness can be adjusted between 0x00 (minimum brightness, 1/16 current) and 0xFF (maximum brightness, 15/16 current). You can also individually control the brightness of each bit. For detailed information about display brightness adjustment and other advanced features (such as GPIO and key scan), please refer to the MAX6954 data sheet.
Table 7. Command summary for quick start examples
| REGISTER (HEX) | COMMAND (HEX) | FUNCTION |
| 0x07 | 0x01 | Enter display test mode |
| 0x07 | 0x00 | Exit display test mode |
| 0x0C | 0xFF | Set all eight digits to use the 14-segment font map |
| 0x04 | 0x01 | Exit shutdown mode, disable blinking and select global intensity control |
| 0x20 | 0x4D | Write "M" to digit 0 |
| 0x21 | 0x41 | Write "A" to digit 1 |
| 0x22 | 0x58 | Write "X" to digit 2 |
| 0x23 | 0x49 | Write "I" to digit 3 |
| 0x24 | 0x4D | Write "M" to digit 4 |
| 0x25 | 0x2D | Write "-" to digit 5 |
| 0x26 | 0x49 | Write "I" to digit 6 |
| 0x27 | 0x43 | Write "C" to digit 7 |
| 0x02 | 0xFF | Set global intensity to full-scale |
Table 8. MAX6954 / MAX6955 partial register address map
| REGISTER | ADDRESS (COMMAND BYTE) | ADDRESS (HEX CODE) | |||||||
| D15 | D14 | D13 | D12 | D11 | D10 | D9 | D8 | ||
| Decode Mode | R // W \ | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0x01 |
| Global Intensity | R // W \ | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0x02 |
| Scan Limit | R // W \ | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0x03 |
| Configuration | R // W \ | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0x04 |
| Display Test | R // W \ | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0x07 |
| Digit Type | R // W \ | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0x0C |
| Intensity 10 | R // W \ | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0x10 |
| Intensity 32 | R // W \ | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0x11 |
| Intensity 54 | R // W \ | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0x12 |
| Intensity 76 | R // W \ | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0x13 |
| Digit 0 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0x20 |
| Digit 1 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0x21 |
| Digit 2 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0x22 |
| Digit 3 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0x23 |
| Digit 4 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0x24 |
| Digit 5 ​​Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0x25 |
| Digit 6 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0x26 |
| Digit 7 Plane P0 | R // W \ | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0x27 |
| Digit 0 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0x40 |
| Digit 1 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0x41 |
| Digit 2 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0x42 |
| Digit 3 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0x43 |
| Digit 4 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0x44 |
| Digit 5 ​​Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 0x45 |
| Digit 6 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0x46 |
| Digit 7 Plane P1 | R // W \ | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 0x47 |
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