How to write to 8 digit led display connected to max7219

[Jim giordano]

I recently received one of the cheap 8 digit led displays run by a max7219.

When I went looking for a demo, all I could find was demos for a max7219 hooked up to an 8x8 led matrix, and using the GLCD graphic display driver.

I can see from these demos how to do the front end. Connect the spi pins for clock and data, and two random pins connected to cs and di. Since I'm not planning on reading the display, I guess DI is unnecessary. From one of the demos (comments are mine and may be incorrect) -

  'Set SPI pins for the Max7219
  #define Max7219_DO    portb.5  ' spi data as set in pps routine
  #define Max7219_SCK   portb.3  ' spi clock as set in pps routine
  #define Max7219_CS    portc.3  ' random pin connected to cs for library to use
  #define Max7219_DI    portb.4  ' do I need to connect a pin if I don't read?

Then I am at a loss for what to do next. Since this not set up as an 8x8 matrix, it doesn't make sense to use the graphic GLCD display driver routines.

What do I use to simply show a number on the display?

I'm going to press on, and I'll figure it out in a few days, but I thought someone must have used one of these before and could save me some time.

[Jim giordano]

edit - deleted as newer code shown later

[stan cartwright]

I am stupid but shouldn't it be

#chip 16F18325,32
#option Explicit
Dim dig(11)
         '76543210
dig( 1)=b'00111111' '0       -      1
dig( 2)=b'00000110' '1     |   |  6   2
dig( 3)=b'01011011' '2       -      7
dig( 4)=b'01001111' '3     |   |  5   3
dig( 5)=b'01100110' '4       -      4
dig( 6)=b'01101101' '5
dig( 7)=b'01111101' '6
dig( 8)=b'00000111' '7
dig( 9)=b'01111111' '8
dig(10)=b'01101111' '9
dig(11)=b'10000000' '.

I got same display but 4 connected and there's a scrolling demo but I never worked out what was happening..ie understood it.
I have two that can be joined and wanted a pixel/led addressable 16x32 display...made from two 8x32.. each an 8x8 unit. Too hard for me.

[mmotte]

I have been using these for a couple years. I almost made a library for them but was distracted and never finished. Just copy in the subs and use. This little project ,I was measuring a positive/ negative voltage on the input to a servo(not the toy ones).

'Plus and minus voltage +-10 vdc input to the adc
'using resistor network of  3 resistors   -  no opamps
' Vcc+5 -<22K >---adc input^|-----<12k>--gnd
' inputvoltage --<80K>------|
'10bit adc reads 300 dec when input touched to gnd
'
' MAX7219 Driver for Great Cow Basic
'
'    using Hardware SPI routines for Great Cow BASIC

'    Copyright (C) 2016 - Mike Otte  ,PearlCity IL

'    This library is free software; you can redistribute it and/or
'    modify it under the terms of the GNU Lesser General Public
'    License as published by the Free Software Foundation; either
'    version 2.1 of the License, or (at your option) any later version.

'    This library is distributed in the hope that it will be useful,
'    but WITHOUT ANY WARRANTY; without even the implied warranty of
'    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
'    Lesser General Public License for more details.

'    You should have received a copy of the GNU Lesser General Public
'    License along with this library; if not, write to the Free Software
'    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

'********************************************************************************
'IMPORTANT:
'THIS FILE IS ESSENTIAL FOR SOME OF THE COMMANDS IN GCBASIC. DO NOT ALTER THIS FILE
'UNLESS YOU KNOW WHAT YOU ARE DOING. CHANGING THIS FILE COULD RENDER SOME GCBASIC
'COMMANDS UNUSABLE!
'********************************************************************************

'Changes:  Aug 2016 written

'Register Address map of commands
'NO-OP    0xX0    0x00
'Digit 0  0xX1    0x01
'Digit 1  0xX2    0x02
'Digit 2  0xX3    0x03
'Digit 3  0xX4    0x04
'Digit 4  0xX5    0x05
'Digit 5  0xX6    0x06
'Digit 6  0xX7    0x07
'Digit 7  0xX8    0x08
'Decode   0xX9    0x09
'Intesity 0xXA    0x0A
'ScanLim  0xXB    0x0B
'Shutdown 0xXC    0x0C
'DispTest 0xXF    0x0F

' 16 bits spi transfer for each digit/COMMANDS
'clock rising - data read
'Load pin low to allow clocked in data

'Sub routines list
'Initialize
'set decode mode
'set intensity of digit x
'set san limit
'writeToDigitX(address,data)
'TurnOn Display


'Changes:

#chip 16F886, 8

#define CS     PortA.5   ' out
#define SCK    PortC.3   'clk out
#define MOSI   PortC.4   'in
#define MISO   PortC.5   'out

  CS = 1
'Set SPI pin directions
dir PORTC.5 out 'SDO
dir PORTC.4 in  'SDI
dir PORTC.3 out 'SCK
dir PORTA.5 out 'SS   load

Dim count,myValue as Word

'Set SPI Mode to master, with fast clock
'SPIMode MasterFast,0
SPIMode ( MasterFast, SPI_CPOL_0 + SPI_CPHA_0 )
  'SSPSTAT = 0x40         ' spi mode was not set correctly in my GC compiler
  'SSPCON1 = 0x20

InitMax7219_7seg

do
  myValue = ReadAD10( AN1 )
  If  myValue >= 297  then
    myValue = (myValue -297)*10/16
    MLED_write(5 ,0x0F)
  else
    myValue = (297- myValue) *10/16
    MLED_write(5 ,0x0A)
  end if


  MLED_Dec(myValue , 4)

  wait 1 s

Loop


sub InitMax7219_7seg

    cs = 1
    wait 100 ms
    'set decode mode
    MLED_write( 0x09 , 0xFF)
    'set intensity 3/4
    MLED_write( 0x0A , 0x06)
    'set scan limit
    MLED_write( 0x0B , 0x07)
    'set display ON
    MLED_write( 0x0C , 0x01)

    For count= 1 to 8
      MLED_write(count,0x0F)  'Clear digits
    next

end sub



sub  MLED_write( cmd , dayta)#NR
  cs = 0
  serBuf = 0x00   'empty bucket
  SPITransfer cmd, serBuf
  serBuf = 0x00   'empty bucket
  SPITransfer dayta, serBuf
  cs = 1
end sub

Sub MLED_Int (In MLEDValue,In NumDig)
  MLEDValueTemp = 0
  MLED_write(NumDig,0x0F)
  MLED_write(NumDig-1,0x0F)
  MLED_write(NumDig-2,0x0F)


  IF MLEDValue >= 100 Then
    MLEDValueTemp = MLEDValue / 100
    MLEDValue = SysCalcTempX
    MLED_write(NumDig ,MLEDValueTemp)
    'NumDig--
  End If
  If MLEDValueTemp > 0 Or MLEDValue >= 10 Then
    MLEDValueTemp = MLEDValue / 10
    MLEDValue = SysCalcTempX
    MLED_write(NumDig-1 ,MLEDValueTemp)
    'NumDig--
  End If
    MLEDValueTemp = MLEDValue
    MLED_write(NumDig-2 ,MLEDValueTemp)

End Sub

Sub MLED_Dec (In MLEDValue as word,In NumDig)
  MLEDValueTemp = 0
  MLED_write(NumDig,0x0F)
  MLED_write(NumDig-1,0x0F)
  MLED_write(NumDig-2,0x0F)
  MLED_write(NumDig-3,0x0F)

  IF MLEDValue >= 1000 Then
    MLEDValueTemp = MLEDValue / 1000
    MLEDValue = SysCalcTempX
    MLED_write(NumDig ,MLEDValueTemp)
    'NumDig--
  End If
  IF MLEDValueTemp > 0 Or MLEDValue >= 100 Then
    MLEDValueTemp = MLEDValue / 100
    MLEDValue = SysCalcTempX
    MLED_write(NumDig-1 ,MLEDValueTemp)
    'NumDig--
  End If
  If MLEDValueTemp > 0 Or MLEDValue >= 10 Then
    MLEDValueTemp = MLEDValue / 10
    MLEDValue = SysCalcTempX
    MLED_write(NumDig-2 ,MLEDValueTemp +0x80)
    'NumDig--
  End If
    MLEDValueTemp = MLEDValue
    MLED_write(NumDig-3 ,MLEDValueTemp)

End Sub

Have fun!

[Jim giordano]

Thanks for that, I'll give it a try shortly.

[Jim giordano]

Well, I think this should work unless I'm missing something important. Or I misunderstand how it works in general.

Yup, I was definately misunderstanding. Bad code deleted. Final working code below.

[Jim giordano]

Well, I tried mmotte's program and got the same results. Any write to the max7219 results in all segments on, just as if I did a "display test ". Either a wiring error, which I've check multiple times, or this unit from China is just no good.

[mmotte]

Might it be the PPS setup?

• SDI must have corresponding TRIS bit set
• SDO must have corresponding TRIS bit cleared
• SCK (Master mode) must have corresponding
TRIS bit cleared

SDO instead of sda(i2c)

  #startup InitPPS, 85
    #define PPSToolPart 16F18325

    Sub InitPPS

            'Module: MSSP1
            RA0PPS = 0x0018    'SCK1 > RA0
            SSP1CLKPPS = 0x0000    'RA0 > SCK1 (bi-directional)
            RA1PPS = 0x0019    'SDO1 > RA1

    End Sub

---

SPIMode gave me trouble those years ago. it is probably ironed out now.
SPIMode Master in yours

SPIMode ( MasterFast, SPI_CPOL_0 + SPI_CPHA_0 ) 'in all the examples in help

--
I see I must add #define SPI_HardwareSPI which we didn't need back then.

73
Mike

[Jim giordano]

You are absolutely correct. I did have the pps screwed up. Too much cut and paste. At least I'm getting something now, not correct, but encouraging! Thanks.

[Jim giordano]

And the final working solution :)

later- nope, still had pps screwed up.
Code deleted. New version farther down.

[Anobium]

An insight

#define SPI_HardwareSPI

You will see this is most demos where SPI is used, or, can be used. There may be a variant of #define SPI_HardwareSPI for a specific device.

What does this do? If you comment this out then the software SPI is supported. This means that you do not need PPS or any SPIMode commands. As software SPImode does not required PPS of the setting of SPMode.

To complete the picture. Some SPI impmentations across the PIC range require SPIBAUD. The demos show how to use but essentially this is a speed adjuster.

---

My rule of thumb advice.

Always, always start with software SPI. Get the device operational then use hardware SPI.

[Jim giordano]

New demo program. Finally got pps right (thanks mmotte)

Edit- found undocumented mode MasterUltraFast, which at 32mhz no longer requires wait between sends, which makes the output MUCH faster.

' 8 digit led to Maxim 7219 demo program
#option Explicit
#chip 16F18325,32
'Generated by PIC PPS Tool for Great Cow Basic for 16F18325
#startup InitPPS, 85
#define PPSToolPart 16F18325
Sub InitPPS
  RC0PPS =     0x0018 'SCK1 > RC0
  SSP1CLKPPS = 0x0010 'RC0 > SCK1 (bi-directional)
  RC1PPS =     0x0019 'SDO1 > RC1
End Sub

#define SPI_HardwareSPI
SPIMode MasterUltraFast, 0
dir portc.0 out  ' clock  sck1
dir portc.1 out  ' data out sdi1
dir porta.2 out  ' cs

#define SpiCS   porta.2  ' cs

getsegs

dim ii,kk
Spics=1

doit b'00001001',b'11111111'  ' decode mode=set all digits to BCD Code B
doit b'00001011',b'00000111'  ' multiplex all eight digits
doit b'00001010',b'00001111'  ' max intensity
erasebcd  ' erase all digits
doit b'00001100',b'00000001'  ' turn on display

doit b'00001111',b'00000001'  ' display test all digits
wait 1 s
doit b'00001111',b'00000000'  ' turn off display test

erasebcd ' clear all digits
wait 500 ms

for ii=1 to 8
  doit ii,ii-1  ' increasing from right to left using bcd
next ii

wait 2 s
erasebcd  ' clear all digits
wait 500 ms

doit b'00001001',b'00000000'  ' set no-decode mode

for ii=1 to 8
  doit ii,seg(9-ii)  ' increasing from left to right using non-bcd
next ii

wait 2 s
erase 'clear all digits
wait 500 ms

doit 8,b'00000001'
doit 7,b'00110111'
doit 6,b'01001111'
doit 5,b'00001110'
doit 4,b'00001110'
doit 3,b'01111110'
doit 2,b'00000000'
doit 1,b'00111110'

wait 2 s
erase ' clear all digits
wait 500 ms

doit b'00001001',b'11111111'  ' decode mode=set all digits to BCD Code B

dim dig(9)  ' bcd value of digit
for kk=1 to 8: dig(kk)=0: next kk
do
  for kk=1 to 8
    dig(kk)++
    if dig(kk)<10 then
      doit kk,dig(kk)
      exit For  ' no more carrys
    end if
    dig(kk)=0
    doit kk,dig(kk)
  next kk  ' loop back and do carry
loop

sub doit(reg,value)
' wait 250 us  ' increase if digits misbehaving
'      not necessary if using MasterUltraFast 
  spics=0
  FastHWSPITransfer reg
  FastHWSPITransfer value
  spics=1
end sub

dim ik
sub erasebcd 'erase all digits when in decode bcd mode
  for ik=1 to 8: doit ik,b'1111': next ik
end sub

sub erase 'erase all digits in non-bcd mode
    for ik=1 to 8: doit ik,0: next ik
end sub

Dim seg(11)
sub getsegs
'         dABCDEFG
seg( 1)=b'01111110' '0       -      1      A
seg( 2)=b'00110000' '1     |   |  6   2  F   B
seg( 3)=b'01101101' '2       -      7      G
seg( 4)=b'01111001' '3     |   |  5   3  E   C
seg( 5)=b'00110011' '4       -      4      E     dp
seg( 6)=b'01011011' '5
seg( 7)=b'01011111' '6
seg( 8)=b'01110000' '7
seg( 9)=b'01111111' '8
seg(10)=b'01111011' '9
seg(11)=b'10000000' '.

end sub