MAX7219 LED Driver (Source Code)
The following is the source code for the MAX7219 LED Driver article. Refer to the complete article for implementation details and explanations.
MAX7219.C
/*
*********************************************************************************************************
* Module : MAX7219.C
* Author : Randy Rasa
* Description: MAX7219 LED Display Driver Routines
*
* The Maxim MAX7219 is an LED display driver thant can control up to 64 individual LEDs, or
* eight 7-segment LED digits, or any combination of individual LEDs and digits. It frees the
* host from the chore of constantly multiplexing the 8 rows and 8 columns. In addition, it
* takes care of brightness control (16 steps), and implements display test and display blank
* (shutdown) features.
*
* The host communicates with the MAX7219 using three signals: DATA, CLK, and LOAD. This
* modules bit-bangs them, but Motorola's SPI interface (or similar interface from other
* manufacturers) may also be used to simplify and speed up the data transfer.
* ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
* DATA _________|D15|D14|D13|D12|D11|D10|D09|D08|D07|D06|D05|D04|D03|D02|D01|D00|______
* ________ __ __ __ __ __ __ __ __ __ __ ________
* CLK |__| |__| |__| |__| |__| |__| |__| |__| |__| |__| |__|
* __________________________________________________________________ ___
* LOAD ______| |__|
*
*
* Implementation Notes:
*
* 1. This module was written and tested using an Atmel AT89C2051 microcontroller, with the
* MAX7219 connected to I/O pins P3.3 (LOAD), P3.4 (CLK), and P3.3 (DATA).
*
* 2. Macros are provided to simplify control of the DATA, CLK, and LOAD signals. You may also use
* memory-mapped output ports such as a 74HC374, but you'll need to replace the macros with
* functions, and use a shadow register to store the state of all the output bits.
*
* 3. This module was tested with the evaluation version of Hi-Tech C-51, using the small memory model.
* It should be portable to most other compilers, with minor modifications.
*
* 4. The MAX7219 is configured for "no decode" mode, rather than "code B" decoding. This
* allows the program to display more than the 0-9,H,E,L,P that code B provides. However,
* the "no decode" method requires that each character to be displayed have a corresponding
* entry in a lookup table, to convert the ascii character to the proper 7-segment code.
* MAX7219_LookupCode() provides this function, using the MAX7219_Font[] array. If you need
* to display more than the characters I have provided, simply add them to the table ...
*
*********************************************************************************************************
*/
/*
*********************************************************************************************************
* Include Header Files
*********************************************************************************************************
*/
#include <8051.h> // microcontroller header file
#include "max7219.h" // MAX7219 header file
/*
*********************************************************************************************************
* Constants
*********************************************************************************************************
*/
#define REG_DECODE 0x09 // "decode mode" register
#define REG_INTENSITY 0x0a // "intensity" register
#define REG_SCAN_LIMIT 0x0b // "scan limit" register
#define REG_SHUTDOWN 0x0c // "shutdown" register
#define REG_DISPLAY_TEST 0x0f // "display test" register
#define INTENSITY_MIN 0x00 // minimum display intensity
#define INTENSITY_MAX 0x0f // maximum display intensity
/*
*********************************************************************************************************
* Macros
*********************************************************************************************************
*/
#define DATA_PORT P3 // assume "DATA" is on P3.5
#define DATA_DDR P3
#define DATA_BIT 0x20
#define DATA_0() (DATA_PORT &= ~DATA_BIT)
#define DATA_1() (DATA_PORT |= DATA_BIT)
#define CLK_PORT P3 // assume "CLK" is on P3.4
#define CLK_DDR P3
#define CLK_BIT 0x10
#define CLK_0() (CLK_PORT &= ~CLK_BIT)
#define CLK_1() (CLK_PORT |= CLK_BIT)
#define LOAD_PORT P3 // assume "LOAD" is on P3.3
#define LOAD_DDR P3
#define LOAD_BIT 0x08
#define LOAD_0() (LOAD_PORT &= ~LOAD_BIT)
#define LOAD_1() (LOAD_PORT |= LOAD_BIT)
/*
*********************************************************************************************************
* Private Data
*********************************************************************************************************
*/
// ... none ...
/*
*********************************************************************************************************
* Private Function Prototypes
*********************************************************************************************************
*/
static void MAX7219_Write (unsigned char reg_number, unsigned char data);
static void MAX7219_SendByte (unsigned char data);
static unsigned char MAX7219_LookupCode (char character);
// ...................................... Public Functions ..............................................
/*
*********************************************************************************************************
* MAX7219_Init()
*
* Description: Initialize MAX7219 module; must be called before any other MAX7219 functions.
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_Init (void)
{
DATA_DDR |= DATA_BIT; // configure "DATA" as output
CLK_DDR |= CLK_BIT; // configure "CLK" as output
LOAD_DDR |= LOAD_BIT; // configure "LOAD" as output
MAX7219_Write(REG_SCAN_LIMIT, 7); // set up to scan all eight digits
MAX7219_Write(REG_DECODE, 0x00); // set to "no decode" for all digits
MAX7219_ShutdownStop(); // select normal operation (i.e. not shutdown)
MAX7219_DisplayTestStop(); // select normal operation (i.e. not test mode)
MAX7219_Clear(); // clear all digits
MAX7219_SetBrightness(INTENSITY_MAX); // set to maximum intensity
}
/*
*********************************************************************************************************
* MAX7219_ShutdownStart()
*
* Description: Shut down the display.
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_ShutdownStart (void)
{
MAX7219_Write(REG_SHUTDOWN, 0); // put MAX7219 into "shutdown" mode
}
/*
*********************************************************************************************************
* MAX7219_ShutdownStop()
*
* Description: Take the display out of shutdown mode.
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_ShutdownStop (void)
{
MAX7219_Write(REG_SHUTDOWN, 1); // put MAX7219 into "normal" mode
}
/*
*********************************************************************************************************
* MAX7219_DisplayTestStart()
*
* Description: Start a display test.
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_DisplayTestStart (void)
{
MAX7219_Write(REG_DISPLAY_TEST, 1); // put MAX7219 into "display test" mode
}
/*
*********************************************************************************************************
* MAX7219_DisplayTestStop()
*
* Description: Stop a display test.
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_DisplayTestStop (void)
{
MAX7219_Write(REG_DISPLAY_TEST, 0); // put MAX7219 into "normal" mode
}
/*
*********************************************************************************************************
* MAX7219_SetBrightness()
*
* Description: Set the LED display brightness
* Arguments : brightness (0-15)
* Returns : none
*********************************************************************************************************
*/
void MAX7219_SetBrightness (char brightness)
{
brightness &= 0x0f; // mask off extra bits
MAX7219_Write(REG_INTENSITY, brightness); // set brightness
}
/*
*********************************************************************************************************
* MAX7219_Clear()
*
* Description: Clear the display (all digits blank)
* Arguments : none
* Returns : none
*********************************************************************************************************
*/
void MAX7219_Clear (void)
{
char i;
for (i=0; i < 8; i++)
MAX7219_Write(i, 0x00); // turn all segments off
}
/*
*********************************************************************************************************
* MAX7219_DisplayChar()
*
* Description: Display a character on the specified digit.
* Arguments : digit = digit number (0-7)
* character = character to display (0-9, A-Z)
* Returns : none
*********************************************************************************************************
*/
void MAX7219_DisplayChar (char digit, char character)
{
MAX7219_Write(digit, MAX7219_LookupCode(character));
}
// ..................................... Private Functions ..............................................
/*
*********************************************************************************************************
* LED Segments: a
* ----
* f| |b
* | g |
* ----
* e| |c
* | |
* ---- o dp
* d
* Register bits:
* bit: 7 6 5 4 3 2 1 0
* dp a b c d e f g
*********************************************************************************************************
*/
static const struct {
char ascii;
char segs;
} MAX7219_Font[] = {
{' ', 0x00},
{'0', 0x7e},
{'1', 0x30},
{'2', 0x6d},
{'3', 0x79},
{'4', 0x33},
{'5', 0x5b},
{'6', 0x5f},
{'7', 0x70},
{'8', 0x7f},
{'9', 0x7b},
{'A', 0x77},
{'B', 0x1f},
{'C', 0x4e},
{'D', 0x3d},
{'E', 0x4f},
{'F', 0x47},
{'\0', 0x00}
};
/*
*********************************************************************************************************
* MAX7219_LookupCode()
*
* Description: Convert an alphanumeric character to the corresponding 7-segment code.
* Arguments : character to display
* Returns : segment code
*********************************************************************************************************
*/
static unsigned char MAX7219_LookupCode (char character)
{
char i;
for (i = 0; MAX7219_Font[i].ascii; i++) // scan font table for ascii code
if (character == MAX7219_Font[i].ascii)
return MAX7219_Font[i].segs; // return segments code
return 0; // code not found, return null (blank)
}
/*
*********************************************************************************************************
* MAX7219_Write()
*
* Description: Write to MAX7219
* Arguments : reg_number = register to write to
* dataout = data to write to MAX7219
* Returns : none
*********************************************************************************************************
*/
static void MAX7219_Write (unsigned char reg_number, unsigned char dataout)
{
LOAD_1(); // take LOAD high to begin
MAX7219_SendByte(reg_number); // write register number to MAX7219
MAX7219_SendByte(dataout); // write data to MAX7219
LOAD_0(); // take LOAD low to latch in data
LOAD_1(); // take LOAD high to end
}
/*
*********************************************************************************************************
* MAX7219_SendByte()
*
* Description: Send one byte to the MAX7219
* Arguments : dataout = data to send
* Returns : none
*********************************************************************************************************
*/
static void MAX7219_SendByte (unsigned char dataout)
{
char i;
for (i=8; i>0; i--) {
unsigned char mask = 1 << (i - 1); // calculate bitmask
CLK_0(); // bring CLK low
if (dataout & mask) // output one data bit
DATA_1(); // "1"
else // or
DATA_0(); // "0"
CLK_1(); // bring CLK high
}
}
MAX7219.H
/*
*********************************************************************************************************
* Module : MAX7219.H
* Author : Randy Rasa
* Description: Header file for MAX7219.C (LED Display Driver Routines)
*********************************************************************************************************
*/
/*
*********************************************************************************************************
* Public Function Prototypes
*********************************************************************************************************
*/
void MAX7219_Init (void);
void MAX7219_ShutdownStart (void);
void MAX7219_ShutdownStop (void);
void MAX7219_DisplayTestStart (void);
void MAX7219_DisplayTestStop (void);
void MAX7219_SetBrightness (char brightness);
void MAX7219_Clear (void);
void MAX7219_DisplayChar (char digit, char character);
This source code is provided as-is, with no warranties or guarantees.
