EPROMs too slow?
 

Hi there,

I own an Amiga 500 with a Kickstart 3.1 original chip. To preserve the original Chip I ordered "AMD 27C400-150" EPROMs and had the data contend of the original Kickstart-chip programmed onto a 27C400-EPROM.

Now, placing the EPROM onto my Kickstart-Switch makes no problem, it is working fine. But placing the EPROM directly into the ROM-Socket on the motherboard (Rev. 6a) results in permanent reboots / black screen. I doublechecked and veryfied; the EPROM`s content matches the Original 100%.

Well, what is that? Is the EPROM too slow? I guess not, since I heard of working EPROMs with a speed of -200. But why does it work in that Kickstart-switch (2 Kick-Sockets, one 74LS00-chip) but not stand-alone?

What could it be? Can I "heal" the problem or can I bin the EPROM? Anyone with an idea? :confused

CU,
A500Man

Was your kick-switcher populated also with the original kickstart chip? If so does the 27c400 work in the switcher alone (the other chip removed)?

Yep,

I tried the Kickstart-switch with (only) the original Chip; it worked.

Does anyone know what the speed of the original Amiga Kickstart 1.3 is?

Hm, the original Kickstart 3.1 is on a "MX23C4100". It does not state a timing, but the MX23C4100 is avaiable in -100, -120 and -150. I fear the Amiga-ROMs are the -100 or -120 types ... Can anyone verify?

CU,
A500Man

Does your 27C400 work in the kick-switcher with empty second socket?
The problem might be caused by lacking pull-up resistors on the motherboard.

150 is too slow for Amiga use sadly.

Get 100ns ones or at worst 120ns.

@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.

What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?

@mfilos: I tried it with an "AMD 27C400-105" a few minutes ago; the same Problem: permanent re-boot.

CU,
A500Man

@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.

What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?

@mfilos: I tried it with an "AMD 27C400-105" a few minutes ago; the same Problem: permanent re-boot. But as I reported: Placing the EPROM on the Kickstart-Switch makes it run.

CU,
A500Man

Seems too strange to be a speed problem... The A4000 mobo has jumper to select 160/200ns speeds - which is far slower than the 105 you are testing with and the A4000 is much faster :crazy

Maybe the ROM socket on your mobo has a loose pin-hole? As it works in your ROM swapper -are the legs of your ROM swapper larger?

hi :-)

what is the version/revision of your A500 motherboard ?
what is the screen color displayed when the eprom is on the motherboard ?

I had the same issue: http://eab.abime.net/showthread.php?p=525862#post525862

If your motherboard revision is 6 or 8 just populate RP106 and RP107.

Jepp,

thank`s yaqube! You gave me an idea and I did some research: the 27C400 has a usual power consumation of 15 mA. The Original Kickstart chips consumes 50 or 60 mA.

Hmpf.

CU,
A500Man

Does any one knows if amga can work with faster kickroms like 50 or 70 nanoseconds ?

regards

As long as they are as fast or faster than the originals, it should work..

Not true, Ive used 140 and it works perfectly fine.

No, access time is set pernamently.

Did you guys ever benchmark rom access speed ? Bustest has also rom access speed (at least bandwidth speed and not latency speed though) but if A4000 is set to 160/200 im guessing indeed everything talked about here is even faster than normal roms.

according to this standard roms (or at least some version of them) are 150ns.

https://www.amiga-stuff.com/hardware/2mbit-maskrom.html

A 68000 bus cycle is 560ns in an Amiga 500. Even if you account for the negligible set-up times for /AS, 150ns ROMs are actually way too fast already…

As mentioned, if Rev.6 or Rev.8, you need to make sure the resistor packs are installed. If it's Rev5 (or Rev.3 probably) then you need a kickstart adapter with the resistors integrated.

With that said, I've had random luck with the EPROMs from far east. I don't know if they are repainted much slower ROMs or just defective, but I've had several not work, even though you can program and verify them.