Upgrading Atari 520STFM TOS

I have recently obtained an ATARI-520STFM computer and have decided that it needs an upgrade on the operating system to allow me to use a Hard disk emulator.

The one I have has 2 roms for the TOS which is version 1.02 and only 2 of the six possible rom positions are populated .

The 1mb eeproms that i have are the 29EE010 which has too many pins!!

The main difference between them is that the ROM for the ST has A16 where /OE is on the 29EE010

so we need to link /OE with /CE so that the output is enabled whenever the chip is enabled and link from pin 2 to pin 24 to get A16 in the right place.

The other issue is the /WE ( write enable ) we need to keep it tied high and we also need to get power from pin 30 to pin 32 .

Don’t worry , we can sort that easily with a couple of links .

For this project you will need 2 pre-programmed 29EE010 ( or pin compatible rom’s/eprom’s 128kx8 ) ROM’s with TOS 1.04 ( one high byte and one low byte )

some link wire ( for the short links I used trimmings from resistor legs and wire wrap wire for the long ones )

So let us begin .

On the 29EE010’s we need to link /OE with /CE and bend the /OE pin out so that it does not go into the socket .

Then solder a link across pin 30,31 and 32.

Solder a long link wire to pin 2 .

Now , place the rom chips in the appropriate sockets making sure that the bent pin stays OUT of the socket .

Now we need to solder the long link on pin 2 into the 8th hole from the edge of the board on the empty rom slot next to the ROM .

Re-assemble the Atari-ST .

You should now have an Atari-STFM with TOS 1.04 ( rainbow TOS )

Have fun with your ST.