One ROM IC for A4000

bebek · 31 December 2014, 08:03

Sorry if it was discussed before but can not find it. I want to use one ROM IC only in A4000 - same way as CD32 uses one. I bet it is possible but how?

Thanks for help.

Locutus · 31 December 2014, 09:06

...Why?

bebek · 31 December 2014, 10:08

Quote:

Originally Posted by Locutus

...Why?

Got my reasons

alexh · 01 January 2015, 01:14

I'm pretty sure it is not possible. A4000 is a fixed 32 bit kickstart. There is a slim chance, changing the "mystery header" default to 16-bit *may* work?

SpeedGeek · 01 January 2015, 18:25

Quote:

Originally Posted by bebek

Got my reasons

If you want to use an A500/A2000 Kickstart ROM switcher that would be one reason (but IMHO not a good reason).

You could try cutting the PCB track to Fat Gary's /STERM and then jumper the /STERM to /DSACK1. You will also need to jumper A1 to the ROM socket(s). Also, the ROM will only work in one of the Sockets. There is NO GUARANTEE this will work so it's at your own risk.

If it does work, then you would need to use ROMs built for the A500/A2000 and those ROMs will operate at 1/2 the speed of the original A4000 ROMs.

So is all of that really worth it?

cpiac64 · 01 January 2015, 18:41

don't work one eprom because one socket have 8 bit even and the other 8 bit pair

single eprom have 16 bit

you can use 2 eprom 27c800 with 3.1 and 3.9 and a switch for select 3.1 or 3.9

bebek · 01 January 2015, 21:19

All I need is using single IC with full 3.1 A4000 rom. Is there a big difference with speed on CD32 comparing to A1200? I have not noticed.

bebek · 01 January 2015, 21:20

Quote:

Originally Posted by SpeedGeek

If you want to use an A500/A2000 Kickstart ROM switcher that would be one reason (but IMHO not a good reason).

You could try cutting the PCB track to Fat Gary's /STERM and then jumper the /STERM to /DSACK1. You will also need to jumper A1 to the ROM socket(s). Also, the ROM will only work in one of the Sockets. There is NO GUARANTEE this will work so it's at your own risk.

If it does work, then you would need to use ROMs built for the A500/A2000 and those ROMs will operate at 1/2 the speed of the original A4000 ROMs.

So is all of that really worth it?

I will think about this one

.Thank you.

Locutus · 01 January 2015, 22:40

I still dont understand it, that sounds like a huge amount of hassle to only having to program 1 ROM

alexh · 02 January 2015, 00:18

I think he must have a faulty motherboard. No other reason to try this.

it's nof a simple jumper change. Even if you work out the motherboard mods, you will get 50% ROM bandwidth

cpiac64 · 02 January 2015, 00:37

i can repair a4000 mainboard if you need

pandy71 · 02 January 2015, 17:09

Ok, perhaps stupid question but can you be more precise? I assume this can be achieved by at least two ways - modify proper PAL on A4000 to force 16 bit cycle where ROM is accessed and second transparent from MB perspective when single 16 bit ROM is shared (trough additional circuitry) between U/L part of 32 bit word (additional circuitry + data latch) - usual ROM cycle is 160ns so even common 70ns FLASH with 20ns delay from circuitry should match ROM speed).

bebek · 02 January 2015, 18:14

Quote:

Originally Posted by cpiac64

i can repair a4000 mainboard if you need

Thank you for an offer but I can repair mainboards and it is not an issue.
I think we have diverted from the topic here. The question is not why? it is how?

.

bebek · 02 January 2015, 18:19

Quote:

Originally Posted by pandy71

Ok, perhaps stupid question but can you be more precise? I assume this can be achieved by at least two ways - modify proper PAL on A4000 to force 16 bit cycle where ROM is accessed and second transparent from MB perspective when single 16 bit ROM is shared (trough additional circuitry) between U/L part of 32 bit word (additional circuitry + data latch) - usual ROM cycle is 160ns so even common 70ns FLASH with 20ns delay from circuitry should match ROM speed).

How more precise?

I hoped it can be done relatively easy way but obviously it does not look like. I do not want additional circuits around as this is against its purpose

.
I would like the idea of modifying proper PAL, sounds good but I will not be able to do it

.

SpeedGeek · 03 January 2015, 15:51

Quote:

Originally Posted by bebek

I would like the idea of modifying proper PAL, sounds good but I will not be able to do it

.

Sorry, there is no proper PAL you can modify, Fat Gary controls ROM access on the A4000.

pandy71 · 07 January 2015, 19:29

Quote:

Originally Posted by speedgeek

sorry, there is no proper pal you can modify, fat gary controls rom access on the a4000.

u152?

SpeedGeek · 08 January 2015, 17:15

Quote:

Originally Posted by pandy71

u152?

The never used 68020 support PLD? You still need to disconnect Fat Gary's /STERM and you still need to connect A1 to the ROM sockets. So why bother with it?

pandy71 · 09 January 2015, 23:32

Quote:

Originally Posted by SpeedGeek

The never used 68020 support PLD? You still need to disconnect Fat Gary's /STERM and you still need to connect A1 to the ROM sockets. So why bother with it?

Yep, and that's why U152 seem to be a good starting point for such conversion - why bother? - not my circus and not my monkeys...

bebek · 10 January 2015, 00:18

I am using this IC for 64MB mod. Thank you for your time guys. Looks like ther is no easy way so it has to stay as it is

.

31 December 2014, 08:03	#1
bebek Registered User Join Date: Dec 2009 Location: Poole UK Posts: 349	One ROM IC for A4000 Sorry if it was discussed before but can not find it. I want to use one ROM IC only in A4000 - same way as CD32 uses one. I bet it is possible but how? Thanks for help. Last edited by bebek; 31 December 2014 at 10:14.

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31 December 2014, 09:06	#2
Locutus Registered User Join Date: Jul 2014 Location: Finland Posts: 1,186	...Why?

01 January 2015, 01:14	#4
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,448	I'm pretty sure it is not possible. A4000 is a fixed 32 bit kickstart. There is a slim chance, changing the "mystery header" default to 16-bit may work?

01 January 2015, 18:41	#6
cpiac64 Registered User Join Date: Apr 2010 Location: Italy Posts: 1,136	don't work one eprom because one socket have 8 bit even and the other 8 bit pair single eprom have 16 bit you can use 2 eprom 27c800 with 3.1 and 3.9 and a switch for select 3.1 or 3.9

01 January 2015, 21:19	#7
bebek Registered User Join Date: Dec 2009 Location: Poole UK Posts: 349	All I need is using single IC with full 3.1 A4000 rom. Is there a big difference with speed on CD32 comparing to A1200? I have not noticed.

01 January 2015, 22:40	#9
Locutus Registered User Join Date: Jul 2014 Location: Finland Posts: 1,186	I still dont understand it, that sounds like a huge amount of hassle to only having to program 1 ROM

02 January 2015, 00:18	#10
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,448	I think he must have a faulty motherboard. No other reason to try this. it's nof a simple jumper change. Even if you work out the motherboard mods, you will get 50% ROM bandwidth

02 January 2015, 00:37	#11
cpiac64 Registered User Join Date: Apr 2010 Location: Italy Posts: 1,136	i can repair a4000 mainboard if you need

02 January 2015, 17:09	#12
pandy71 Registered User Join Date: Jun 2010 Location: PL? Posts: 2,867	Ok, perhaps stupid question but can you be more precise? I assume this can be achieved by at least two ways - modify proper PAL on A4000 to force 16 bit cycle where ROM is accessed and second transparent from MB perspective when single 16 bit ROM is shared (trough additional circuitry) between U/L part of 32 bit word (additional circuitry + data latch) - usual ROM cycle is 160ns so even common 70ns FLASH with 20ns delay from circuitry should match ROM speed).

10 January 2015, 00:18	#19
bebek Registered User Join Date: Dec 2009 Location: Poole UK Posts: 349	I am using this IC for 64MB mod. Thank you for your time guys. Looks like ther is no easy way so it has to stay as it is .

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