Thanks for them video really useful. I think the reason why it’s needed in both half’s is due to the top data line not being connected and effectively left floating. So some reads will come from the top block and others will come from the bottom block. So you need the code in both.
I read somewhere that on the BBC motherboard ROM sockets that Pin 1 (which is address A14 on these EEPROM chips) is not connected. If that's correct it means it is floating, so the EEPROM may randomly think A14 is either high or low. This may explain why the chip works for you if you copy a 16K rom into both the lower and upper blocks of the chip. Then it doesn't matter whether A14 is high or low, as the data in both halves is the same. I am trying some AT28C256-15PC chips I got off eBay without much success. On close inspection the four chips I bought all look a little different, leaving me suspicious they're not genuine. I will probably try ordering some more from another seller. Do you recall exactly what model you bought?
Cant remember now, but yes one of the pins I had to wire to +5v since then i modified the settings on my eprom blower and I use old 16k eproms and work a treat.
Wish I’d seen this a few months back, went through the same pain with 32k eeproms. Same result but different method, some on stardot told me to copy the 16k Rom file to itself which then gave me a 32k file to upload so same principle as copying the block buyout doing in cmd line as a file merge/copy.
Thanks for them video really useful. I think the reason why it’s needed in both half’s is due to the top data line not being connected and effectively left floating. So some reads will come from the top block and others will come from the bottom block. So you need the code in both.
Or add 5v to one of the pins
brilliant video thank you!
I read somewhere that on the BBC motherboard ROM sockets that Pin 1 (which is address A14 on these EEPROM chips) is not connected. If that's correct it means it is floating, so the EEPROM may randomly think A14 is either high or low. This may explain why the chip works for you if you copy a 16K rom into both the lower and upper blocks of the chip. Then it doesn't matter whether A14 is high or low, as the data in both halves is the same. I am trying some AT28C256-15PC chips I got off eBay without much success. On close inspection the four chips I bought all look a little different, leaving me suspicious they're not genuine. I will probably try ordering some more from another seller. Do you recall exactly what model you bought?
Cant remember now, but yes one of the pins I had to wire to +5v since then i modified the settings on my eprom blower and I use old 16k eproms and work a treat.
Keep them coming.
I will
That was great 👍
Wish I’d seen this a few months back, went through the same pain with 32k eeproms. Same result but different method, some on stardot told me to copy the 16k Rom file to itself which then gave me a 32k file to upload so same principle as copying the block buyout doing in cmd line as a file merge/copy.
Yes it also depends what chips you use there is easy way to frig this programmer so you can use old 27128s that is actually what I normally use now.