Making use of EEprom as a character ROM

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

With many AVR projects the EEprom sees very little use a large percentage
is unused.
When I built the dot matrix clock I used it as a character ROM to free up flash.
Here I am building on that using a Arduino Nano as a test device with MAX7219
dot matrix displays.
This first program puts characters 32 through to 122 into EEprom.

You will notice a comment at character 95 up till this character the first byte is zero
I intend to compress the rom by using only 7 bytes this I will do in the next version
and then I will take it to 5 bytes as the last two are also zero.

Regards Paul

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

Now I have reduced the fonts to 5 bytes as the first , seventh & eight byte was zero
This allows us to put all the most used characters into less than 1K of eeprom

Regards Paul

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

Good idea. Thank you for sharing Very Happy

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

Now a program using 5 bytes for the rom
It is set up for 8 characters using 8 MAX7219s
by increasing the text variable and setting Numdis variable
to the number of MAX7219s many more can be used

Later I will mix a MAX7219 seven segment display with the dot matrix ones

Note this can be used with the free version of Bascom as it only compiles to 3608 bytes

Regards Paul

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

Now a program that asks for how many characters in your display
and sets the variable.
This is sent to a prompt on the terminal screen of your computer
after this you can type a message then hit enter and it will be
displayed on the dot matrix display.

Note this can not be used with the free version
but if you comment out the marked section
and set the Numdis variable in the code it can be.

Regards Paul

pratik · Joined: 13 Oct 2005 Posts: 55

Thanks for sharing the codes
I was testing it on max7219 8x8 led matrix 4 in 1 module with UNO 328p board
Tested both codes but nothing is working
Checked all the wiring many time as specified in program.
As you specified I burn the eeprom program first then I check the eeprom contains & verified it after burning the main program
On serial terminal program it showing
How many Characters in display ?
But after entering any key nothing is displayed on the 8x8 led matrix display

I also merge eeprom program & main program but no luck.
I know I am doing something wrong but not able to find out what

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

Hello Pratik

When it asks "How many Characters in display" you then enter the number of them
for example if you use one 4 character module press 4 then hit the enter key
4 will then be displayed on the module
After this you can enter text then press enter for it to be displayed.

Regards Paul