Very simple ext. mem. question.

[Analyzer]

Hi there,

I need to store 100Kb data in an external eeprom and display sentences with my 2*40 lcd.But unfortunately i have no idea how to connect and use external memory with 16F877.Can somebody show me a way to learn how to use memories with ccs? I really need a tutorial :( It is urgent, i need to complete my project as soon as possible :(
Thanks in advance.

Analyzer.

[Guest]

[snoopy]

Consider to use SPI memory. 25Cxxx.
connect 16f877 25Cxxx
sck 18 6 sclk
sdi 23 2 so
sdo 24 5 si
(1 pin) 1 cs

you need to configure, SPI mode

setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_CLK_DIV_4);

for the moment you need to configure
spi_clk_div_x (xxx= 4, 8, 16). Depend
of the crystal frequency and and speed of your memory.
EX: CRYSTAL 20Mhz, Memory speed 8MHz 20/xxx(4)=5MHz
SPI tranfert is 5MHz.

To write in eeprom;
use fonction
Write SPI(zzz); zzz is the value to send in SPI
write_spi() is a fonction in CCS software


First
output_low(cs);
write_spi(0x06); // mode WREN for Microchip memory
output_high(cs);

output_low(cs);
write_spi(0x02); //mode write
write_spi(addh); //address high
write_spi(addl); //address low
write_spi(value);//data to put in memory
CAN STOP or write_spi(value);
output_high(cs);

CAN STOP if you write one data only put high the cs.

if you want to write some value just add value,
like you want and the address wil increment automatically.

That is the basic way to wriTe in external memory.

but the best way is to use pointer for addr an value.

Try it!

[Neutone]

If you settle on an external EEPROM you should concider the block read/write method and write your routines to access entire strings rather than bytes. If you start with this aproach you will save time in the end. Find out what the block size is for the part you chose and determine how many complete strings will fit in a block. Setup you string loading routine to use accept a string index that sequentialy addresses the strings in the external part.

[Analyzer]

Hi There,

Thank you for all great help.I would like to use 24xxx memories because i can not find 25xxx memories in my country :( I also can not find any model for 25xxx at Proteus 6??
By the way i will read avr. 100~150 characters per second from mem in my project.I will use 877 and 4 mhz clock.
How can i achive my goal with 24xxx?

Thanks a lot again.

Analyzer.

[Neutone]

[Analyzer]

Thank you for all your help.I referenced from ccs manual and i connected a 24LC128 to 877 and i used standart 24128.h library.It works fine but i changed pull-up resistors to 470k instead of 1k.

Analyzer.