Four 8X8 Dot matrix display module

For this example, we are using the Wangdd22 MAX7219 Dot Matrix Module For Arduino Microcontroller 4 In 1 Display with 5 pins $10.99.
There are many similar Chinese-made modules.

Driving the with Bit-banged Serial generated using the Z80 PIA on my Z80 board. could easy adapt for any PIO or 8-bit output deivce.

Amazon link https://www.amazon.com/dp/B07FNCY6DZ?psc=1&ref=ppx_yo2ov_dt_b_product_details

Basic Unit Operation

The Max7219 uses an SPI-type serial interface, with serial in, serial out, Clock, and Chip Enable pins. The module has 5 pins on each end, two power, one side serial in, Clock, Chip Enable, second side two power, serial out, Clock, Chip Enable to cascade to other units.

These Modules are arranged in an 8-bit row configuration.

*01234567 ROW is one 8-bit byte 0####### 1####### 2####### 3####### 4####### 5####### 6####### 7#######

My routine sends out data 4 rows at a time, until all 8-bytes of Data have been loaded into each display unit.

For my Demo I am writing the data in upside down so the input data moves from right to left, with the left most display being 0, and the last 3, while the data is inverted I still load the rows from 0 to 8 into the MAX719

buffer format:
display 0 row 0, display 1 row 0, display 2 row 0, display 3 row 0
display 0 row 1, display 1 row 1, display 2 row 1, display 3 row 1
display 0 row 2, display 1 row 2, display 2 row 2, display 3 row 2display 0 row 3, display 1 row 3, display 2 row 3, display 3 row 3display 0 row 4, display 1 row 4, display 2 row 4, display 3 row 4
display 0 row 5, display 1 row 5, display 2 row 5, display 3 row 5display 0 row 6, display 1 row 6, display 2 row 6, display 3 row 6display 0 row 7, display 1 row 7, display 2 row 7, display 3 row 7
For the shifting buffer, I add one extra 8-bit byte to each column.
repeats 8 x display 0 row 0, display 1 row 0, display 2 row 0, display 3 row 0, buffer 0 row 0

Initialize the MAX7219 this code sets 10 parameters from the variable set in C "init_max8x8" into all four MAX7219 chips.

SECTION code_user
PUBLIC _spi_init
EXTERN _init_max8x8
EXTERN _spi_init; Bit 0 = Clock; Bit 1 = Data; Bit 2 = Chip enable
_spi_init: push ix push hl ld hl, _init_max8x8 ld a, 0xcf ;set PIO port A output out (0x02), a ld a, 0xf8 ; bit mask firt three bits output out (0x02), a ld a, 0x05 out (0x00), a ld b, 0x05 ;start first looplp1: ld c, 0x04; Note add address outlp2: ld d, 0x08 ld e, (hl) ; Out address bytelp3: ld a, 0x00 ;Set chip enable Clear data bit, and Clock state out (0x00), a rlc e ;Rotate Bit to left c jp c, out_1 ;check if 1 in Carry Bit out (0x00), a jp endlp3out_1: set 1, a ; set Data Bit high out (0x00), aendlp3: set 0, a ;Bit 0 Clock state high out (0x00), a dec d jp nz, lp3 lp4: ld d, 0x08 inc hl ld e, (hl) ; out data bytelp5: ld a, 0x00 ;Set chip enable Clear data bit, and Clock state out (0x00), a rlc e ;Rotate Bit to left c jp c, ot1 ;check if 1 in Carry Bit out (0x00), a jp endlp4ot1: set 1, a out (0x00), a ; set Data Bit highendlp4: set 0, a ;Bit 0 Clock state high out (0x00), a dec d jp nz, lp5 dec hl dec c jp nz, lp2 ; End loop2 set 2, a out (0x00), a dec b jp z, exitlp inc hl inc hl jp lp1exitlp: set 2, a out (0x00), a pop hl pop ix ret

Write Data data stored in "_max8x8_buffer" into the four Max 7219

SECTION code_user
PUBLIC _spi_buffer_write
EXTERN _max8x8_buffer
EXTERN _spi_buffer_write ; Bit 0 = Clock; Bit 1 = Data; Bit 2 = Chip enable
_spi_buffer_write: push ix push hl ld hl, _max8x8_buffer ld a, 0xcf ;set PIO port A output out (0x02), a ld a, 0xf8 ; bit mask firt three bits output out (0x02), a ld a, 0x05 out (0x00), a ld b, 0x08 ;start first looploop1: ld c, 0x04; Note add address outloop2: ld d, 0x08 ld e, b ; Out address byteloop3: ld a, 0x00 ;Set chip enable Clear data bit, and Clock state out (0x00), a rlc e ;Rotate Bit to left c jp c, out1 ;check if 1 in Carry Bit out (0x00), a jp endloop3out1: set 1, a ; set Data Bit high out (0x00), aendloop3: set 0, a ;Bit 0 Clock state high out (0x00), a dec d jp nz, loop3 loop4: ld d, 0x08 ld e, (hl) ; out data byteloop5: ld a, 0x00 ;Set chip enable Clear data bit, and Clock state out (0x00), a rlc e ;Rotate Bit to left c jp c, outone ;check if 1 in Carry Bit out (0x00), a jp endloop4outone: set 1, a out (0x00), a ; set Data Bit highendloop4: set 0, a ;Bit 0 Clock state high out (0x00), a dec d jp nz, loop5 inc hl dec c jp nz, loop2 ; End loop2 set 2, a out (0x00), a dec b jp z, exitloop jp loop1exitloop: set 2, a out (0x00), a pop hl pop ix ret

Here is code for scrolling display routines

; This code shifts data in our expanded buffer, then copies it to the main buffer

SECTION code_user
PUBLIC _shift_buffer
EXTERN _max8x8_buffer
EXTERN _max8x8_buffer_t
EXTERN _shift_buffer
_shift_buffer: push ix push hl ld ix, _max8x8_buffer_t ld b, 0x08 ;start first looploop1: or a ; clear carry flag rl (ix + 4) rl (ix + 3) rl (ix + 2) rl (ix + 1) rl (ix + 0) inc ix inc ix inc ix inc ix inc ix dec b jp NZ, loop1 ld a, 8 ld hl, _max8x8_buffer_t ld de, _max8x8_bufferloop2: ld bc, 4 ldir inc hl dec a jp nz, loop2 pop hl pop ix ret

; for creating Animation in the scrolling text I created a second expanded shift buffer, that copies to the main buffer; by alternating the two can create simple two-frame animation see scrolling example 2
SECTION code_user
PUBLIC _shift_buffer2
EXTERN _max8x8_buffer
EXTERN _max8x8_buffer_v
EXTERN _shift_buffer2
_shift_buffer2: push ix push hl ld ix, _max8x8_buffer_v ld b, 0x08 ;start first looploop1: or a ; clear carry flag rl (ix + 4) rl (ix + 3) rl (ix + 2) rl (ix + 1) rl (ix + 0) inc ix inc ix inc ix inc ix inc ix dec b jp NZ, loop1 ld a, 8 ld hl, _max8x8_buffer_v ld de, _max8x8_bufferloop2: ld bc, 4 ldir inc hl dec a jp nz, loop2 pop hl pop ix ret

; this code is for the first initial copy of the expanded buffer to the display buffer
SECTION code_user
PUBLIC _cp_buffer
EXTERN _max8x8_buffer
EXTERN _max8x8_buffer_v
EXTERN _cp_buffer
_cp_buffer2: push ix push hl ld a, 8 ld hl, _max8x8_buffer_v ld de, _max8x8_bufferloop1: ld bc, 4 ldir inc hl dec a jp nz, loop1 pop hl pop ix ret

; copy second expanded buffer to display buffer
SECTION code_user
PUBLIC _cp_buffer2
EXTERN _max8x8_buffer
EXTERN _max8x8_buffer_v
EXTERN _cp_buffer2
_cp_buffer2: push ix push hl ld a, 8 ld hl, _max8x8_buffer_v ld de, _max8x8_bufferloop1: ld bc, 4 ldir inc hl dec a jp nz, loop1 pop hl pop ix ret
cop

C example code using the assembly routines, cretes a scrolling display of letters.

/* Z80 PIO max7219 8x8 matrix display */
#include "z80_pio.h"#include "font-8x8.h"#include <z80.h>#include <stdlib.h>#include <stdio.h>
// MAX7219 SPI LED Driver#define MAX7219_TEST 0x0f // in real code put into a .h file#define MAX7219_BRIGHTNESS 0x0a // in real code put into a .h file#define MAX7219_SCAN_LIMIT 0x0b // in real code put into a .h file#define MAX7219_DECODE_MODE 0x09 // in real code put into a .h file#define MAX7219_SHUTDOWN 0x0C // in real code put into a .h file
extern void spi_buffer_write( void );extern void spi_init( void );

char init_max8x8[10] = { 0x0f, 0x00, 0x0a, 0x00, 0x09, 0x00, 0x0b, 0x0f, 0x0c, 0x01 };char max8x8_buffer[256] ;unsigned char text[16] = { 0x2e, 0x2e, 0x2e, 0x2e, 0x5a, 0x2d, 0x38, 0x30, 0x20, 0x43, 0x50, 0x55,0x2e, 0x2e, 0x2e, 0x2e };

int test = 0;
int main(){// SPI interface 16 bit data streamint x,y, z; char i, j, data, address;
// make sure out PIO is set correctz80_outp( Z80_PIO_A_CTL, Z80_PIO_M3); // set mode z80_outp( Z80_PIO_A_CTL, 0xF8);z80_outp( Z80_PIO_A, 0x05);z80_outp( Z80_PIO_B_CTL, Z80_PIO_M1); // set mode

spi_init();z = 0;
j = 0;
while ( j < 100 ){
// load text to be displayed// scrolling effect

for( x=0; x < 8; x++) { for( y=0; y < 4; y++) { max8x8_buffer[ (4 * x) + y ] = console_font_8x8[ 8 * text[y + z] + (7 - x) ]; // (7 - x) reverse order in which we load row data to flip character } }
spi_buffer_write( );
z80_delay_ms(500);
z++; // z is the shift of characters from the start of character string data.
if ( z > 11 ) z = 0;
}
return 1;}

This code is an example of created two frame scrolling Animation,

/* Z80 PIO max7219 8x8 matrix display */
#include "z80_pio.h"#include "font-8x8.h"#include <z80.h>#include <stdlib.h>#include <stdio.h>
// MAX7219 SPI LED Driver#define MAX7219_TEST 0x0f // in real code put into a .h file#define MAX7219_BRIGHTNESS 0x0a // in real code put into a .h file#define MAX7219_SCAN_LIMIT 0x0b // in real code put into a .h file#define MAX7219_DECODE_MODE 0x09 // in real code put into a .h file#define MAX7219_SHUTDOWN 0x0C // in real code put into a .h file
extern void spi_buffer_write( void );extern void spi_init( void );extern void shift_buffer( void );extern void shift_buffer2( void );extern void cp_buffer( void );
char init_max8x8[10] = { 0x0f, 0x00, 0x0a, 0x00, 0x09, 0x00, 0x0b, 0x0f, 0x0c, 0x01 };char max8x8_buffer[64], max8x8_buffer_t[64], max8x8_buffer_v[64] ;unsigned char text[16] = { 0x2e, 0x2e, 0x2e, 0x2e, 0x5a, 0x2d, 0x38, 0x30, 0x20, 0x43, 0x50, 0x55,0x2e, 0x00, 0x01, 0x2e };unsigned char text2[16] = { 0x2e, 0x2e, 0x2e, 0x2e, 0x5a, 0x2d, 0x38, 0x30, 0x20, 0x43, 0x50, 0x55,0x2e, 0x02, 0x03, 0x2e };
int test = 0;
int main(){// SPI interface 16 bit data streamint x, y, z; char i, j, data, address, a1;
// make sure out PIO is set correctz80_outp( Z80_PIO_A_CTL, Z80_PIO_M3); // set mode z80_outp( Z80_PIO_A_CTL, 0xF8);z80_outp( Z80_PIO_A, 0x05);z80_outp( Z80_PIO_B_CTL, Z80_PIO_M1); // set mode

spi_init();
a1 = 0;z = 0;
j = 0;
for( x=0; x < 8; x++) { for( y=0; y < 5; y++) { max8x8_buffer_t[ (5 * x) + y ] = console_font_8x8[ 8 * text[y + z] + (7 - x) ]; //(7 - x) } }
for( x=0; x < 8; x++) { for( y=0; y < 5; y++) { max8x8_buffer_v[ (5 * x) + y ] = console_font_8x8[ 8 * text2[y + z] + (7 - x) ]; //(7 - x) } }

cp_buffer( );spi_buffer_write( );
z = 4;while ( j < 100 ){

for(j=0;j<8;j++){z80_delay_ms(125);if (a1 == 0) { shift_buffer2(); shift_buffer(); spi_buffer_write( ); a1 = 1; }else{ shift_buffer(); shift_buffer2(); spi_buffer_write( ); a1 = 0; }}
z++;if (z > 15) z = 0;
y = 5;for( x=0; x < 8; x++) { max8x8_buffer_t[ (5 * x) + 4 ] = console_font_8x8[ 8 * text[z] + (7 - x) ]; //(7 - x) }y = 5;for( x=0; x < 8; x++) { max8x8_buffer_v[ (5 * x) + 4 ] = console_font_8x8[ 8 * text2[z] + (7 - x) ]; //(7 - x) }
}
return 1;}