Dongguan Yijia Optoelectronics Co., Ltd. , https://www.everbestlcdlcms.com
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, 7-segment LED displays.
For more information about MAX6954, please refer to the MAX6954 data sheet.
Application notes "Quick Start: Using MAX6954 to Drive a 16-Segment LED Display" and "Quick Start: Using MAX6954 to Drive a 14-Segment LED Display" Similar to this article, they explain how to configure the MAX6954 to drive 16- and 14-segment displays, respectively. 
Enlarged display Figure 1. The MAX6954 drives a 7-segment display circuit
A common application of the MAX6954 is to drive up to 16-bit 7-segment monochrome LEDs. This application note guides the user how to connect the MAX6954 to a 7-segment display and how to configure its internal registers to control the display of hexadecimal characters.
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. The application note "Charlieplexing-Reduced Pin-Count LED Display MulTIplexing" discusses this technique. Table 1 is the connection table between MAX6954 and 7-segment display. This table is compatible with the multiplexing configuration of MAX6954 and its built-in font of hexadecimal characters. The letters in Table 1 correspond to the segment identifiers in Figure 2. Figure 1 is a schematic diagram of the MAX6954 driving a 16-bit 7-segment display.
Table 1. Connection table with 16-bit 7-segment display Digit O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18 0,
0a CC0 - 1a - 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 1,
1a - CC1 1a - 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 2,
2a 1a - CC2 - 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 3,
3a 1a - - CC3 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 4,
4a 1a - 1b 1c CC4 - 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 5,
5a 1a - 1b 1c - CC5 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 6,
6a 1a - 1b 1c 1d 1dp CC6 - 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp 7,
7a 1a - 1b 1c 1d 1dp - CC7 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g 2dp
After connecting the MAX6954 and the 7-segment display, you can use the display test mode 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. 
Figure 2. Segment identification of 7-segment display
After completing the connection check, you need to set the MAX6954 register value as required to drive the 7-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. Everyone displays blanking, selects a 7-segment font and sets the maximum number of scan digits, that is, eight bits. The MAX6954 can be set to a mode that drives a 7-segment display by writing 0xFF to register 0x0C. The default value of the decoding mode register (0x01) applies to 7-segment displays.
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 7-segment font 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 sixteen 7-segment digits: 0, 1, 2, 3, 4, 5, 6, 7, 0a, 1a, 2a, 3a, 4a, 5a, 6a, 7a 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 7 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 Intensity10a 1/16 (min on), digits 1a and 0a 0x14 0 0 0 0 0 0 0 0 Intensity32a 1/16 (min on), digits 3a and 2a 0x15 0 0 0 0 0 0 0 0 Intensity54a 1/16 (min on), digits 5a and 4a 0x16 0 0 0 0 0 0 0 0 Intensity76a 1/16 (min on), digits 7a and 6a 0x17 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 Digit 0a Blank digit, both planes 0x68 0 0 1 0 0 0 0 0 Digit 1a Blank digit, both planes 0x69 0 0 1 0 0 0 0 0 Digit 2a Blank digit, both planes 0x6A 0 0 1 0 0 0 0 0 Digit 3a Blank digit, both planes 0x6B 0 0 1 0 0 0 0 0 Digit 4a Blank digit, both planes 0x6C 0 0 1 0 0 0 0 0 Digit 5a Blank digit, both planes 0x6D 0 0 1 0 0 0 0 0 Digit 6a Blank digit, both planes 0x6E 0 0 1 0 0 0 0 0 Digit 7a Blank digit, both planes 0x6F 0 0 1 0 0 0 0 0
The configuration register (0x04) is used to set the entry and exit of the shutdown mode, control the blinking 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 power-down mode or normal operating 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 blinking 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 blink timing phase (read-only-writing to this bit will be ignored). Table 3. Configuration register format CONFIGURATION
REGISTER
DATA BIT DATA BIT LABEL STATE FUNCTION D7 P 0 P1 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 Intensity76a 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 active-low CS D4 T 0 Blink timing counters are unaffected. 1 Blink timing counters are reset on the rising edge of active-low 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
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 7-segment display remains blanked (see Table 2 and Figure 3). 
Figure 3. 7-segment display font
The MAX6954 has a built-in hexadecimal font for 7-segment displays, with 7 digits representing hexadecimal characters, and the 8th digit for selecting whether to light the decimal point (DP) (see Table 4). The data register has two levels, P0 and P1. Each display bit is represented by 2 bytes in the memory, one byte is located at P0 and the other is located at P1 (see Table 7). The data register is a mapped address mode, so each bit of data can be updated in P0 (registers 0x20 to 0x2F), P1 (registers 0x20 to 0x4 F), and can also be updated in two levels (registers 0x60 to 0x67). The data in the data register does not directly control the display of each segment in the 7-segment display. Instead, it is used to address the character generator that stores 7-segment 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 4. Digital type data register format MODE ADDRESS CODE (HEX) REGISTER DATA D7 D6 D5 D4 D3 D2 D1 D0 7-segment mode, writing digit data to use font map data with decimal place unlit 0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F 0 Bits D6 to D0 select font character 7-segment mode, writing digit data to use font map data with decimal place lit 0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F 1 Bits D6 to D0 select font character
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 for display multiplexing. 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 MAX6954 driver to display Maxim / Dallas sales department telephone: 1 800 629 4642. 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 0x2F. Use the font diagram in Figure 3 to get the code corresponding to each character.
Table 5. Phone 800.629.4642 examples REGISTER ADDRESS (HEX) DIGIT CHARACTER FONT MAP EQUIVALENT CODE DECIMAL HEX 0x20 0 C 0000 1100 0x0C 0x28 0a A 0000 1001 0x0A 0x21 1 1 0000 0001 0x01 0x29 1a 1 0000 0001 0x01 0x23 3 8 0000 1000 0x08 0x2B 3a 0 0000 0000 0x00 0x24 4 0 1000 0000 0x80 0x2C 4a 6 0000 0110 0x06 0x25 5 2 0000 0010 0x02 0x2D 5a 9 1000 1001 0x89 0x26 6 4 0000 0100 0x04 0x2E 6a 6 0000 0110 0x06 0x27 7 4 0000 0100 0x04 0x2F 7a 2 0000 0010 0x02
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. Please refer to the MAX6954 data sheet for more information on display brightness adjustment and other advanced features (such as GPIO and key scan)
Table 6. Routine command set REGISTER
(HEX) COMMAND
(HEX) FUNCTION 0x07 0x01 Enter display test mode 0x07 0x00 Exit display test mode 0x04 0x01 Exit shutdown mode, disable blinking and select global intensity control 0x20 0x0C Write "C" to digit 0 0x28 0x0A Write "A" to digit 0a 0x21 0x01 Write "1" to digit 1 0x29 0x01 Write "1" to digit 1a 0x23 0x08 Write "8" to digit 3 0x2B 0x00 Write "0" to digit 3a 0x24 0x80 Write "0." to digit 4 0x2C 0x06 Write "6" to digit 4a 0x25 0x02 Write "2" to digit 5 0x2D 0x89 Write "9." to digit 5a 0x26 0x04 Write "4" to digit 6 0x2E 0x06 Write "6" to digit 6a 0x27 0x04 Write "4" to digit 7 0x2F 0x02 Write "2" to digit 7a 0x02 0xFF Set global intensity to full-scale
Table 7. MAX6954 / MAX6955 partial register address map REGISTER ADDRESS (COMMAND BYTE) ADDRESS
(HEX CODE) D15 D14 D13 D12 D11 D10 D9 D8 Decode Mode R / active-low W 0 0 0 0 0 0 1 0x01 Global Intensity R / active-low W 0 0 0 0 0 1 0 0x02 Scan Limit R / active-low W 0 0 0 0 0 1 1 0x03 Configuration R / active-low W 0 0 0 0 1 0 0 0x04 Display Test R / active-low W 0 0 0 0 1 1 1 0x07 Digit Type R / active-low W 0 0 0 1 1 0 0 0x0C Intensity 10 R / active-low W 0 0 1 0 0 0 0 0x10 Intensity 32 R / active-low W 0 0 1 0 0 0 1 0x11 Intensity 54 R / active-low W 0 0 1 0 0 1 0 0x12 Intensity 76 R / active-low W 0 0 1 0 0 1 1 0x13 Intensity 10a R / active-low W 0 0 1 0 1 0 0 0x14 Intensity 32a R / active-low W 0 0 1 0 1 0 1 0x15 Intensity 54a R / active-low W 0 0 1 0 1 1 0 0x16 Intensity 76a R / active-low W 0 0 1 0 1 1 1 0x17 Digit 0 Plane P0 R / active-low W 0 1 0 0 0 0 0 0x20 Digit 1 Plane P0 R / active-low W 0 1 0 0 0 0 1 0x21 Digit 2 Plane P0 R / active-low W 0 1 0 0 0 1 0 0x22 Digit 3 Plane P0 R / active-low W 0 1 0 0 0 1 1 0x23 Digit 4 Plane P0 R / active-low W 0 1 0 0 1 0 0 0x24 Digit 5 ​​Plane P0 R / active-low W 0 1 0 0 1 0 1 0x25 Digit 6 Plane P0 R / active-low W 0 1 0 0 1 1 0 0x26 Digit 7 Plane P0 R / active-low W 0 1 0 0 1 1 1 0x27 Digit 0a Plane P0 R / active-low W 0 1 0 1 0 0 0 0x28 Digit 1a Plane P0 R / active-low W 0 1 0 1 0 0 1 0x29 Digit 2a Plane P0 R / active-low W 0 1 0 1 0 1 0 0x2A Digit 3a Plane P0 R / active-low W 0 1 0 1 0 1 1 0x2B Digit 4a Plane P0 R / active-low W 0 1 0 1 1 0 0 0x2C Digit 5a Plane P0 R / active-low W 0 1 0 1 1 0 1 0x2D Digit 6a Plane P0 R / active-low W 0 1 0 1 1 1 0 0x2E Digit 7a Plane P0 R / active-low W 0 1 0 1 1 1 1 0x2F Digit 0 Plane P1 R / active-low W 1 0 0 0 0 0 0 0x40 Digit 1 Plane P1 R / active-low W 1 0 0 0 0 0 1 0x41 Digit 2 Plane P1 R / active-low W 1 0 0 0 0 1 0 0x42 Digit 3 Plane P1 R / active-low W 1 0 0 0 0 1 1 0x43 Digit 4 Plane P1 R / active-low W 1 0 0 0 1 0 0 0x44 Digit 5 ​​Plane P1 R / active-low W 1 0 0 0 1 0 1 0x45 Digit 6 Plane P1 R / active-low W 1 0 0 0 1 1 0 0x46 Digit 7 Plane P1 R / active-low W 1 0 0 0 1 1 1 0x47 Digit 0a Plane P1 R / active-low W 1 0 0 1 0 0 0 0x48 Digit 1a Plane P1 R / active-low W 1 0 0 1 0 0 1 0x49 Digit 2a Plane P1 R / active-low W 1 0 0 1 0 1 0 0x4A Digit 3a Plane P1 R / active-low W 1 0 0 1 0 1 1 0x4B Digit 4a Plane P1 R / active-low W 1 0 0 1 1 0 0 0x4C Digit 5a Plane P1 R / active-low W 1 0 0 1 1 0 1 04D Digit 6a Plane P1 R / active-low W 1 0 0 1 1 1 0 0x4E Digit 7a Plane P1 R / active-low W 1 0 0 1 1 1 1 0x4F
Quick Start: Using MAX6954 to drive a 7-segment LED display
Abstract: This article aims to help engineers quickly master the use of the MAX6954 to drive 7-segment monochrome LED drivers.