Upgrading the TOS on a 520STFM
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.