TOS EPROMS

atari-korps · Post by **atari-korps** » Wed Aug 04, 2004 11:18 pm

Hi, I have decided to go down the root of purchasing my own EPROM burner and I wanted to know what size EPROMs should I be using for the various Atari TOS chips

I know the Mega STE took 27C040 and I know I need two (one HI and one Low) but thatÂ’s itÂ…

Is it ok to have bigger than 254K? I have seen some larger ones for sale locally and they are 4MB in size.. does this matter?

Could someone tell me what the EPROMS the 1040 STE and MegaST4 uses?

Cheers

Post by **Greenious** » Thu Aug 05, 2004 8:13 am

With the exception of F030, no atari uses larger eproms than 27C010.

Using larger eproms is only useful if you intend to do various dualtos installments.

(Mega) ST most often use 6x27C256 EPROMs, or 2x1 mbit mask rom.

(Mega) STE uses 2x1mbit mask eprom, or 2x27C010.

TT uses 4x27C010

F030 uses one 16bit wide 44 pin PLCC that is otherwise equivalent to 27C040

atari-korps · Post by **atari-korps** » Thu Aug 05, 2004 9:11 am

Greenious wrote:With the exception of F030, no atari uses larger eproms than 27C010.

Using larger eproms is only useful if you intend to do various dualtos installments.

(Mega) ST most often use 6x27C256 EPROMs, or 2x1 mbit mask rom.

(Mega) STE uses 2x1mbit mask eprom, or 2x27C010.

TT uses 4x27C010

F030 uses one 16bit wide 44 pin PLCC that is otherwise equivalent to 27C040

thanks,
i'm just trying to work out what the last three digits mean...

27C256 = 256KB ?
27C040 = 4MB ?
27C010 = 1MB ?

so buying some "15 x UV erasable 4Mb 512k x 8 CMOS EPROMs " would be a waste of money then?

also can you tell me if it's the same for the 1040 STE?

Post by **Greenious** » Thu Aug 05, 2004 9:33 am

atari-korps wrote:
27C256 = 256KB ?
27C040 = 4MB ?
27C010 = 1MB ?

so buying some "15 x UV erasable 4Mb 512k x 8 CMOS EPROMs " would be a waste of money then?

also can you tell me if it's the same for the 1040 STE?

The last 3 digits tells you the size in bits. (NOT bytes)

A 27C010 is a 1 megabit eprom (128 kilobytes).

No, not really a waste of money, you can use them aswell. But take note of the number of pins on the EPROM, and the pinout. ST/STE follows the JEDEC pinout standard, but some eproms can have different pinout.

Also, 1 mbit mask ROM, is a 28 pin chip. but a 1mbit EPROM is a 32pin chip.

27C256/512 are also 28 pin chips.

atari-korps · Post by **atari-korps** » Thu Aug 05, 2004 11:09 am

oh i see...
cheers...
yes i have just opened up a 1040 ste and a mega st4
and i noticed that the mega st EPROMs are the smaller 28pin
where as my 1040 ste has the larger EPROMs

ok so if i buy these EPROMS, can i then sinmply 'burn' them? or is there going to be an address problem because of there size?
forgive me but i have never looked deeply into EPROMs before...

warerat · Post by **warerat** » Thu Aug 05, 2004 10:04 pm

atari-korps wrote:oh i see...
cheers...
yes i have just opened up a 1040 ste and a mega st4
and i noticed that the mega st EPROMs are the smaller 28pin
where as my 1040 ste has the larger EPROMs

ok so if i buy these EPROMS, can i then sinmply 'burn' them? or is there going to be an address problem because of there size?
forgive me but i have never looked deeply into EPROMs before...

You'll need a programmer to burn the EPROMs.

If you're going to use the 128K EPROMS (2-chip) take the TOS ROM file and split it into odd and even. Then each file gets burned on to one chip.

My secondhand 520ST had disk TOS ROMs, so I got six spare 27512 EPROMs I had (didn't have any 27256) and took a TOS 1.4 image and split it into odd/even. Then I had to divide those files into 32K so it would fit on each chip. My 520ST has the A15 pin on the 27512 hooked up to VCC so I had put the 32K image in the top half of the 64K. Worked like a charm after I figured out which group of three of six sockets were on UDS/LDS (odd/even - lo/hi) .

In theory I could upgrade to TOS 2.06 using the exisiting sockets by using 4 27512 EPROMs and cutting the traces where A15 goes on the socket and hooking it up to the real A15. Then I'd have to add a modified decoder (I'd use a GAL) for the $E00000 select. One of these days I'll get around to it or if I'm lazy I'll just use 2 27C010's I got.

Post by **Greenious** » Thu Aug 05, 2004 10:15 pm

atari-korps wrote:oh i see...
cheers...
yes i have just opened up a 1040 ste and a mega st4
and i noticed that the mega st EPROMs are the smaller 28pin
where as my 1040 ste has the larger EPROMs

ok so if i buy these EPROMS, can i then sinmply 'burn' them? or is there going to be an address problem because of there size?
forgive me but i have never looked deeply into EPROMs before...

If you decide to get larger EPROMs than supported by the hardware in Atari, they will automatically be "banked" since the hardware only outputs adresslines for a 1 mbit eprom at best.

So, if we take a 27C040 vs a 27C010 for example....

A 27C010 is 1mbit, 8 bits wide, giving us 128kilobytes of read only memory. To adress that, we need 17 adress lines.

A 27C040 is 4mbit, 8 bits wide, giving us 512 kilobytes of read only memory. To adress that, we need 19 adress lines.

But the hardware in ST(E) only has 17 adresslines allocated for the TOS roms. 2 adress lines are not connected.

These 2 will have to be connected elsewhere, like to a switch, to select "bank" or which part of the eprom we will use.

So yes, using a larger eprom does bring some adressing issues you have to consider.

tssn · Post by **tssn** » Wed Dec 01, 2004 9:40 am

If you're going to use the 128K EPROMS (2-chip) take the TOS ROM file and split it into odd and even. Then each file gets burned on to one chip.

How do you split the ROM file???

gwEm · Post by **gwEm** » Tue Dec 21, 2004 11:48 am

http://www.atari-forum.com/ftopic5040.html

has a tool for splitting the files

or your eprom software does it