28pin to 32pin EPROM conversion

Upgrade or replace the ROM.
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exxos
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28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:12 pm

Information taken from the archives on my website http://www.exxoshost.co.uk/atari/last/tos/index.htm to expect bad pictures :twisted:


"SOCKET METHOD"

I am going to upgrade the TOS to RAINBOW TOS 104. I upgrade the TOS using regular EPROM which have been programmed with the TOS 104 images already.

It is noted that the EPROM's are 1MBit and are slightly longer than the original TOS ROMS's. The original TOS ROM's were OTP (one time programmable mask roms) and have less pins than EPROM's. Some wiring is needed to adapt them for ST use.

I use regular turn pin sockets for this upgrade. I find it makes things nice and neat. However, if you decide to use the sockets rather than doing all the wiring directly to the EPROM, then the ST metal shield will not seat correctly as the addition of the socket makes them too high to fit. So a small hole would have to be cut in the metal shield. There are many options though this socket example is the one which I shall go with in this series.

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First we must bend up and outwards the pin on the left of the IC. looking from the bottom, we count 8 pins up from the bottom left upwards. Notice the "notch" of both the socket and the IC are at the top of the image. If you get this part wrong you will wire your EPROM upside down!

Trim the bend lag back if needed. Also when you solder the bottom right pin try to only solder to the upper part of the pin and not allow the solder to run down the leg else it will not fit into the socket!

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Above we now have a top view of the finished wire.

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And the side view of the bent pin

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and the side view of the other connection. Notice the solder is only at the top of the leg as mentioned earlier!

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Now to start on the socket!

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Notice the IC notch is to the right of the image. We need to cut off level the 2 end pins. Do not cut them off totally as we need to solder some wires to them. This overhang the sockets on the motherboard and if not cut , could short out onto the PCB.

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Top 3 pins on the left are soldered together and linked to the top right pin only.

Then counting 8 pins up from the bottom left we link to the second pin down from the top right.

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Done! Slot the EPROM's into the sockets and that's it!

The EPROM on the left I took the wire directly over the EPROM as the black wire on the right is a little harder to see.

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Side view of the 2 finished EPROM's

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Now they are slotted into the motherboard. Notice the overhang the IC sockets by 2 pins!

As mentioned before, the EPROM on the bottom of the picture is physically higher than the ST's metal shield so some slight metal editing is needed, or you could always removed the socket on the motherboard and solder out new sockets in place. Or just do all the wiring directly to the EPROM though I find overall the outlined method to be the neatest way, other than some small metal editing!
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: 28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:14 pm

"LAZY ASS METHOD"

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For those who want to solder the EPROM directly it follows much the same as the socket method. however where the plane bare wire and black wire meet, they much not touch, this can be tricky in pushing the wire into the IC socket on the motherboard.

top 3 pins get soldered as before to the top right pin. Then the second pin down from the top on the right has a loose connection the other end where the EPROM pin was bent up.

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Notice the black wire (EPROM BENT PIN UP) is not touching the bare wire.

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We now have a nice RAINBOW TOS 104 installed and working :-)

I like rainbow tos as the FUJI is all different colours like a rainbow! and its even animated too!
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: 28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:16 pm

BETTER SOLUTIONS

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viewtopic.php?f=16&t=272
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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kolli
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Re: 28pin to 32pin EPROM conversion

Post by kolli » Sun Jan 13, 2019 7:35 am

Thanks for this! I followed the description and it worked like a charm. At least after some flaws...

At the first photo you can't really see that the chip is positioned on his back. This mislead me to bending and soldering the wrong side. It became clear with the following picture. But my chips were OTP, so I didn't stumble over the missing UV window in the first picture...

On the photo with the markings "cut 2 pins" the description says "the IC tab is to the left". This got me irritated a lot, because you can see that the IC notch is clearly on the right. English is not my native language, so I don't know if tab and notch mean different things. But what other than the notch would be so significant that you British guys would invent a word for it? :-)

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Re: 28pin to 32pin EPROM conversion

Post by exxos » Sun Jan 13, 2019 11:20 am

Looks like it was a typo and should have said right. Will correct it later.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: 28pin to 32pin EPROM conversion

Post by tzok » Sun Jan 13, 2019 12:50 pm

exxos wrote:
Fri Feb 02, 2018 2:12 pm
It is noted that the EPROM's are 1MBit and are slightly longer than the TOS ROMS's. The original TOS ROM's were OTP (one time programmable) and have less pins than EPROM's.
That technically is not correct. OTP EPROMs are programmable and thus have the same pin count as the UV-EPROMs. Only difference between UV-EPROMs and OTP-EPROMs is the case (expensive ceramic/epoxy, vs. cheap plastic). Original TOS was supplied on Mask ROMs, which were "programmed" during the die manufacturing process. The difference in socked is only present in 1Mb ROMs vs. EPROMs. 256k TOS ROM chips used in older STs (6-pack) have the same case as their equivalent UV/OTP EPROM chips (27C256).

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Re: 28pin to 32pin EPROM conversion

Post by exxos » Sun Jan 13, 2019 12:53 pm

tzok wrote:
Sun Jan 13, 2019 12:50 pm
exxos wrote:
Fri Feb 02, 2018 2:12 pm
It is noted that the EPROM's are 1MBit and are slightly longer than the TOS ROMS's. The original TOS ROM's were OTP (one time programmable) and have less pins than EPROM's.
That is technically not correct. OTP EPROMs are programmable and thus have the same pin count as the UV-EPROMs. Only difference between UV-EPROMs and OTP-EPROMs is the case (expensive ceramic/epoxy, vs. cheap plastic). Original TOS was supplied on Mask ROMs, which were "programmed" during the die manufacturing process. The difference in socked is only present in 1Mb ROMs vs. EPROMs. 256k chips used in older STs (6-pack) have the same case.
I'm talking about the 1mb otp mask roms in the ST which are "shorter" and have less pins than eproms. So I don't see how that is not correct ? Its well known.

The 256K ROM's are physically the same size as the original mask roms. That is well known also. The 1mb eproms are longer than the original Atari roms. This is why you have to "hack" 1mb roms as I show in my guide as they don't physically fit! I sell the adapter pcb as shown if people want that solution, also I sell 256K kits which are eproms which replace the original roms.

EDIT:

I think your getting confused over what I was saying so I updated the text in case it confuses anyone else in the future.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

Forgottenmyname
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Re: 28pin to 32pin EPROM conversion

Post by Forgottenmyname » Sun Jan 13, 2019 1:20 pm

At least I know that I can now use 6 x 27c256 for a 6 chip tos. Just need to get 1.04 split into 6 parts as I have about 50 of them.

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Re: 28pin to 32pin EPROM conversion

Post by tzok » Sun Jan 13, 2019 1:29 pm

OTP stands for One Time Programmable, Mask-ROMs (or just ROMs) are not programmable at all. The program is embedded into them during the die lithography process (like any other custom chip or ASIC for short). This kind of memory doesn't need any extra programming pins, and this is a type of memories Atari was originally using for TOS. OTP EPROMs are ordinary EPROMs just in different case, without a "window" to erase them with UV light. OTP EPROMs need to be programmed after the chip factoring process, and this is done in exactly the same way as with EPROMs, and thus they have to have exactly the same pin count as equivalent EPROMs. OTP EPROMs are still called EPROMs (despite E is for Erasable) as they are exactly the same technology as EPROMs (and they actually still can be erased but with the x-rays instead of UV light). There were also PROMs, which were programmed in slightly different way - by burning connections in a memory matrix. These connections were called micro-fuses, and thus we have a "fuse bits" in some micro-controllers (despite they are EEPROM type cells nowadays). The term PROM is historically reserved for this type of fuse-based one time programmable memories (and not for OTP EPROMs).
Forgottenmyname wrote:
Sun Jan 13, 2019 1:20 pm
At least I know that I can now use 6 x 27c256 for a 6 chip tos. Just need to get 1.04 split into 6 parts as I have about 50 of them.
You can use either PP's TOS based software for this:
http://atari.8bitchip.info/astopensw.php (look for ROMSPLIT)
or use mine, Windows based (first split into 3 parts, 64kB each, then split each into Lo/Hi... or the other way round):
https://github.com/TzOk83/CartMan
...and remember that CartMan uses Little Endian nomenclature, while Atari ST is a Big Endian machine. So a Low byte in my program is a High byte in Atari ST (so file "tosxxxyy_ROM0_H.bin" should be used to program a "L0" chip and a file "tosxxxyy_ROM2_L.bin" do program a "H2" chip).

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Re: 28pin to 32pin EPROM conversion

Post by exxos » Sun Jan 13, 2019 1:37 pm

Yes I'm aware of all that thanks. The mask ROMs could not be reprogrammed and are one time programmable. As to method of "programming" is not relivent to this thread and the user doesn't need to know in depth info about it all, they just need to know they can't reprogram mask ROMs and need to adapt eproms to fit which can be reprogramed.

What you are doing is going into great detail over things which are not relivant to fitting the ROMs. If people want to look into all the exact how's and why's then they can do that. But why does the person need to know about blowing fuses in chips etc ? They don't. Its just over complicating a otherwise simple task.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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