Chip Sectored and replacement

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Chip Sectored and replacement

Postby miki02131 » Sat Jan 24, 2009 2:50 pm

Two 256k Chips: One is sectored as 4X64k and the other is structured as 3X64k, 1X32k, 2X8k, 1X16k. Now, the question is: can these two chips be flashed by the same bin and be used interchangeably?

Thanks,

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Postby Karlsweldt » Sat Jan 24, 2009 3:20 pm

If the two chips are the older DIPP type, there would be one "high" and one "low" entity. Or could be marked "odd" and "even". One chip had the "odd" bit count 1, 3, 5, 7, etc. while the other chip had the "even" bit count 0, 2 ,4 ,6, etc. memory design.
Normally in a 28-pin package. They must be in their respective sockets. They were from the days when memory structure was large, and there was room for only one 'bank' of pages.. either odd or even. That series came to an end, in the latter years of the '386' processor. Today's BIOS chips are about 1/3 the size of one older DIPP, and can have over 2 Mb of hi/lo memory bit structure.
If there is a foil label on the tops of the chips covering a small window, they cannot be flashed with a disk. An 'eraser' using a UV lamp would be needed, then a reprogramming 'burner' would write the new data. The foil label is peeled away to expose a tiny tinted window above the memory structure. Commonly known as EPROM chips.
You could sometimes have success with replacing the BIOS chips with newer models, as long as it was the same "family".. either AMI or Award/Phoenix.
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Postby miki02131 » Sat Jan 24, 2009 7:33 pm

Karl,

Is there any similarity between EPROM formatting and hdd formatting? If so, like any file can be written to a FAT or NTFS drive, it might be possible to flash two differently formatted chips with the same bios file.
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Postby evasive » Sun Jan 25, 2009 3:15 am

If they are pin-compatible and the flash program does recognize what it is, I don't see why not.
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Postby Karlsweldt » Sun Jan 25, 2009 1:41 pm

A hard drive will write data to the next available sector for whatever length the string file is. But with EPROM programming, you must address a specific bit register with the desired "0" or "1". The design is ROM, with specific addresses.. and if the wrong info is in the bit register, the system won't work properly.
You would need a 'burner' deck like the one in this link, and of course the program data chart for the chip. Here is some basics on EPROM 'burning'. With those chips having small windows, you must be careful not to expose them to strong UV light sources.. or the program can be corrupted easily! They have to be treated like the old-fashioned glass photography plates.
The modern BIOS chips don't have that 'window' for erasure.. they are designed to allow a program input through a secondary BASIC chipset that controls the erasure and writing through an external program.. via floppy disk, most commonly. The modern BIOS setups have two memory structures.. the ROM for default setups, and the PROM for BIOS configurations according to machine usage.
I still have my 'erasing oven', but foolishly sold my programming deck. :(
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