sh5, memory ampliation,...

**Alexvrb** · September 29th, 2004, 15:03

No, you misunderstand. I thought I already straightened this up. There IS a version of the SH5 that is pin and instruction compatible with at least one major SH4 package. That is a true statement. However, I yet again reiterate the fact that the SH4 in the Dreamcast is not just a standard SH7750 chip. It is custom. So therefore just because the SH5 in question is pin compatible with some kind of SH4 and instruction compatible with the "SH4 instruction set" doesn't automatically mean it is fully compatible with the DC's SH4. It may not support the extra instructions. Not to mention that the pin design/layout could be custom too. So it's not suitable for upgrading the DC, even if you could overcome any other problems.

I would like to mention (I think I said it in the DC2 thread) that if you were building a completely new system, you could emulate the DC's SH4 on the SH5. So you could make a new inexpensive console that is backwards compatible. Unfortunetely that's yet another crazy pipe dream.

**Rufus** · September 29th, 2004, 21:22

Just for curiousity sake, could you provide a link which describes the differences between a standard SH7750 and the customized version used in the DC?

***quzar*** · September 29th, 2004, 22:00

Also, even if there are SH5s that are pin-compatible, they still are not compatible with the prehipherals the DC uses (internal ones). ALSO just because there are SH5s that are pin compatible with A SH4 doesnt mean there are ones pin compatible with the sh4 used in teh DC.

**Alexvrb** · September 29th, 2004, 22:51

[quote author=Rufus link=board=hardware;num=1095614726;start=0#11 date=09/29/04 at 22:22:23]Just for curiousity sake, could you provide a link which describes the differences between a standard SH7750 and the customized version used in the DC?[/quote]
You mean do I feel like digging up some Sega documents or whatever, that I probably shouldn't have access to anyway even if I found them? No, not particularly. BlackAura and others would know more about it anyway.

***quzar*** · September 30th, 2004, 04:33

I think the only person who would know what ops are in the SH4 DC as opposed to the SH4 standard is Rand.

**bender** · September 30th, 2004, 08:56

I see it now, Alexvrb, quzar

. Thnks for the explanation. I haven't read that the dc's sh4 it's different (my english sometimes really sucks :-[ ) So the only possible thing to have really a powerfull and compatible system it's to try to build a new system with some kind of motherboard that already supports the sh5 and adding all the needed peripheals and emulate the whole dreamcast. Seems very expensive and a hard task, though :-/

**elefas** · October 5th, 2004, 13:55

By reading the official sega documents on dreamcast hardware outline, in the system specifications section I came across the following:

? 16MB Main memory(Can expand to a maximum of 32MB)
? 8MBTexture memory(Can expand to a maximum of 16MB)
? 2MB Boot ROM
? 128KB Flash memory
? 2MB audio memory(Can expand to a maximum of 8MB)

The parenthesis show that the memory installed on DC can be expanded, otherwise why should they mention it? There are also some diagrams, I am not a hardware expert but what I understood is that it uses 2 64Mbit (4 x 512k x 32bit) blocks of RAM connected to the SH4 cpu. The problem is that SH4 cpu has 12 address pins available for memory addressing and 64bit data bus in which half pins are connected to the 1st module of RAM and the other half to the second module. So if I am right, we cant connect lets say another 2 same RAM modules (not enough space for the data bus) but the 12bit address bus can support memory modules twice as big as the default ones. In conclusion we may expand the dc main memory by replacing the default modules with others of twice capacity, the address lines can support it. However I don't know how we could "inform" the dreamcast to use this extra space (I suppose it needs bios upgrade).

Ohh, the above are just some simple thoughts. An experienced hardware guy probably will get more by reading the documentation.

**Alexvrb** · October 5th, 2004, 14:49

Yes, memory expansion is more feasible than replacing the processor. I've been told that you wouldn't even need to modify the BIOS, although I've been told the opposite as well. Maybe someone will do it eventually, but unfortunetely any sort of complicated internal modification would never see widespread use. The only way you could get a large portion of people to upgrade would be through an external expansion, and I don't see anything like that happening either.