Amiga kickstart eprom

[scoobyatgb]

Could some one help I have just got my self a eprom programmer I would like too make my own kickstart Rom it say that you use a 27c400 does that mean you can use any one as I have heard that it need too be the right speed is that right if so would would I look for too get the right one if so we're would I get them from also could I use a different eprom or does it need too be that one and are they just push them in and not need too do any thing else

 

[Jameson]

Good question mate - I have a Willem Eprom programmer and have programmed heaps of different types of EPROMs and EEPROMs - all successfully.... EXCEPT 27C400s - they are the ONLY eprom I cannot burn reliably. I have asked why on occasion, but no one has ever answered so I just gave up.

I hope you have better luck.

 

[roy_bates]

yes mate thats what they are,get 120ns parts mate.

and no,you dont need to do anything else there pin compatible.

and use an external piower supply for the programmer(12 volt at about 1.5 amps)


best of luck

 

[scoobyatgb]

We're the best place too look for them just eBay or is there other places you can get them from

 

[Magic]

As far as the 27C400's go I have used both AMD and Intel versions and they both work fine. Its' a little tricky though. You have to fill the entire 512k EPROM. To make 1.2 or 1.3 (256k) work in an A500/2000 with a 27C400 you would have to load the kickstart twice to make it work. You will also have to perform a "byte swap" in your programmer software. Before attempting to program always verify that the EPROM is erased first.

 

[roy_bates]

27c400 are 512k,maybe you got confused with 27c800's? because kickstart 1.3 only fits on a 27c400 twice not four times.

byte swapping is true.

 

[Magic]

You are correct sir, it has been WAY too long... Thank you!

I forgot that you have to split the 512k kickstart.bin image in to Hi and Lo 256k images to burn kickstarts for A1200-A4000's. The A500/2000 uses one kickstart ic only. Each 256k Hi and Lo section of a 512 kickstart must be doubled in to a pair of 27c400's to work in an A1200/4000(t). In otherwords an eprom that is half empty will not boot, that's what I was trying to say Does that make sense?

 

[scoobyatgb]

Thanks for that what does the byte swap do also do you it when one is loaded or when both are and we're is a good place too get them from

 

[Jameson]

I have a collection of byte swapped images ready for programming if you cannot find them.

 

[scoobyatgb]

Thanks for that when you put your files into the program ready for burning does it tell you when it is full also if you do other EPROMs do you all ways have too byte swap or is that just on amiga ones and also do you have too make sure they are all ways filled up

sorry too too ask so many questions I am just too this

 

[roy_bates]

Thanks for that when you put your files into the program ready for burning does it tell you when it is full also if you do other EPROMs do you all ways have too byte swap or is that just on amiga ones and also do you have too make sure they are all ways filled up

sorry too too ask so many questions I am just too this

dont worry bud,its normal to ask questions

you can do the byte swapping at the programmer there is an option for that

no,it dont tell you its full...most of the time its just working out the file size and see if the part you have fits the bill.but it does have a progress bar and it checks it after.
basically you look up the part your using and work out its capacity,then you fill it with a file of that size.
but,its not always true.

no,alot machines dont need byte swapping,and yes there are other machines that need it too.

 

[scoobyatgb]

Ok so how do you work out the size of the eprom does it work a amiga disk

 

[Magic]

I am pretty rusty, but I will try and help some more.

A500 - A2000 with 1.2 or 1.3 ROM is 256k. This will directly fit in to a 27C200 or 2 times in to a 27C400

A500 - A2000 with 2.04+ ROM is 512k. This will fit once in a 27C400

It gets a lot more complex with machines with 2 ROMs like the A1200 and A4000(t). These machines use the same 512k kickstart size but it is split in to LO and HI ROMS that are each are 256k. In other words for an A1200 you would need (2) 27C200 ROMS for a direct fit. If you use 27C400 ROMs then you have to double up to fill the second half of the ROM. In theory you could use two different kickstarts in a pair of 27C400's on an A1200 or A4000 but I don't know how you would access the second one. Both 1.2 and 1.3 should fit a 27C400 for an A500, does that make sense?

I hope this helps. As far as the byte swap goes try doing a Google search for "big endian to little endian conversion"

 

[roy_bates]

I am pretty rusty, but I will try and help some more.

A500 - A2000 with 1.2 or 1.3 ROM is 256k. This will directly fit in to a 27C200 or 2 times in to a 27C400

A500 - A2000 with 2.04+ ROM is 512k. This will fit once in a 27C400

It gets a lot more complex with machines with 2 ROMs like the A1200 and A4000(t). These machines use the same 512k kickstart size but it is split in to LO and HI ROMS that are each are 256k. In other words for an A1200 you would need (2) 27C200 ROMS for a direct fit. If you use 27C400 ROMs then you have to double up to fill the second half of the ROM. In theory you could use two different kickstarts in a pair of 27C400's on an A1200 or A4000 but I don't know how you would access the second one. Both 1.2 and 1.3 should fit a 27C400 for an A500, does that make sense?

I hope this helps. As far as the byte swap goes try doing a Google search for "big endian to little endian conversion"

i dont think you have to double up for the 1200 and 4000 im sure you can leave blank areas,they are split as well as byte swapped.

if you want to have two kickstart images you just use one of the pins on each eprom to split the rom to read from the higher or lower portion by holding it high or low via a voltage between ground and + at boot time.
i wont explain how at the mo but its fairly easy.

same sort of way you would split a eprom for duel boot on,say a c64 duel boot system.but without the split and byte swapping...

ive done this myself using two 27c800 on a 1200...

 

[scoobyatgb]

Thanks sounds great Roy could you let me know how you would do that on a amiga 1200 could you get 1.3 rom too work and could you do three in one rom and how do you know what pin it is

 

[roy_bates]

ok,if connect pin 1 (A18 on a 27c800) via a 4.7 or 10k resistor to +5 volts it will load the high portion of the rom...if you connect pin 1 to ground itll load the lower portion at boot time.

so....if you have pin one connected to a switch it would be connected to the center pole,and the other pins on the switch would be connected to ground and the other end to +5 volts via a resistor to hold the line low or high,see?

so...if it was for a 1200 you simply do the same but with two 27c800 and a switch thats duel throw duel pole as in six pins to handle both eproms at the same time.


then...its a case of merging the files to fit the eprom in windows after making them in a program like remus...
i wont explain how to do that part as it would just be a wall of text and would take me ages to explain how,honest...
ill leave that part for others to explain,modules and what sequence there loaded into the amiga etc,there is a thread here that explains it somewhat.

as for 1.3...never tried it but i think it would work.with that said i cant see a reason why it couldn't be divided into three or four and just work out the size of the rom needed to hold all the files.and what pins to use to divide it up.
on mine,i wanted to try to divide it by two for 3.1 and custom 3.9...never seen the need for 1.3 on a 1200.

 

[scoobyatgb]

That's great so can you do it without the switch and do it by a key press like the reset keys and holding them down longer too switch between the Roms

 

[roy_bates]

yes, i imagine its possible.

 

[scoobyatgb]

Any idea how you would do that

 

[ej2095]

Considering a custom rom as well with all the latests updates...

As i am sure kickstart is copyrighted.. and i already own 0s3.9 and 3.5 and the original kickstart chips, BUT i dont have a programmer etc

Whats the legality of asking some one to make these chips for my self (Not asking as don't want to get into trouble)

Thank you