28C256 EEPROM Writer

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28C256 32k EEPROM Writer

Raspberry PI PCB

email: info@homebrew8088.com

This is a simple homemade EEPROM writer that any one can make.

To make a writer It requires the following

  • Breadboard w/jumpers

  • 2 - MCP23S17 16-bit SPI I/O Expander

  • Raspberry PI

*note the project is 100% directed towards the 28c256 EEPROM's. but you should be able to adapt the concept to other sizes of EEPROM's

Schematics

32k ROM Unlock Code 8088 assembly

ORG 0X0000


;Setup 8255

MOV AL, 0X80 ;MODE 2 PORT B OUTPUT

OUT 0X63, AL ;WRITE TO 8255 COMMAND PORT

MOV AL, 0XAA ;WRITES 0XAA TO PORT 0X60

OUT 0X60, AL ;


MOV AX, 0XF000 ;SET UP DATA SEGMENT

MOV DS, AX ;

MOV BYTE [0X5555], 0XAA ;UNLOCK BYTES

MOV BYTE [0X2AAA], 0X55 ;

MOV BYTE [0X5555], 0X80 ;

MOV BYTE [0X5555], 0XAA ;

MOV BYTE [0X2AAA], 0X55 ;

MOV BYTE [0X5555], 0X20 ;


MOV BYTE [0X7FF0], 0X20 ;LEAVES A MARKER IN THE END OF THE ROM


HLT