The first thing was to test the output of the address-lines. Additionally I created a simple “16 bit line-sniffer” with 16 small LEDs and two ULN2803 darlington drivers to protect the “sniffed” bus from too much current consumption. To be sure that everything works as expected, I first build up everything on a breadboard. But for the address-lines I only need output and no input lines so I can use two 74HC595 shift register to get up to 16 address-lines with only 3 GPIOs used on the ♜. My preferred ♜ has only 20 GPIO pins that seems to be too less for my programmer. The programmer should be used by a serial connection, so I need 2 more lines for RX and TX. I also need 8 data lines and 3 additional lines for /WE, /OE and /CE. ![]() The 28C64 and 28C256 are 28 pin DIP chips and have up to 14 address lines (28C256). ![]() I'm quite familiar with the AVR ATMega micro-controllers, especially with the Arduino boards and so I decided to build my own programmer based on the Atmega328 ♜. In preparation for my own homebrew 6502 system I need a possibility to write data on a 28C64 or eventually the 28C256 EEPROM. I hope this is the right place for this topic.
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