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BOS ROM exists at rom slot 6 and is decoded exactly (no repeat).
DFxx is decoded by the Vortex RAM Expansion (for BOS) and uses xx0xxxxx xxxxxxxx xxxxxxxx xxxxxxxx (same as other ROM expansions).
The FBBD port is decoded as: xxxxx0xxx0xxxx0x
This means just 3 bits are decoded for it.
Data written to the vortex RAM doesn't write through to main RAM.
On Reset the BOS rom is activated.
Bits 7 and 6 written to FBBD are ignored. Bit 5 is for enabling the ram expansion. Bit 2,1,0 set the bank.
Bit 3 is documented as enabling and disabling the ROM, but I found it didn't work exactly like that.
If bit 3 is set to 1, and upper ROM is enabled with port 7fxx, then ROM on the Vortex RAM Expansion is enabled in the range &c000-&7fff.
If bit 3 is set to 1, and lower ROM is enabled with port 7fxx, then ROM on the Vortex RAM expansion is enabled in the range &c000-&7fff.
If bit 3 is 0, then normal operation happens. ROM is visible in the range &c000-&7fff only if ROM slot 6 is selected and the upper rom is enabled with port 7fxx. When bit 3 is 0, the rom is not visible in the range &0000-&3fff at any time.
It is possible this part of my (arnoldemu) vortex ram expansion is broken, but all other operation works perfectly and the BOS rom is active at reset time and can be used as normal.
On my (arnoldemu) vortex ram expansion, the bus has the value 0. It seems the vortex is forcing the value on the bus.
== Description ==
A RAM expansions expansion card from made by [[Vortex Computersysteme|Vortex]], mounted between CPC464 CPC 464/664 mainboard and CPU/Gate Array. It won't fit on CPC664, CPC6128the cost-down CPC 464, CPC 6128 or CPC+ boards. The card is not compatible with the standard [[dk'tronics]]-sytle style [[Standard Memory Expansions]].
Sold in different sizes of RAM as '''SP 64''', '''SP 128''', '''SP 256''', '''SP 320''' and '''SP 512'''. Resulting in a maximum RAM size of 576K (64K internal, plus 512K external). The smaller SP64-SP320 versions can be upgraded to SP512 by mounting additional RAM chips in the spare sockets. There is also a cut-down version, '''SP 64/M''', which contains only 64K RAM, no BOS ROM, and which isn't upgradable.
Image:Vortex_PCB_Bottom.jpg|Vortex Expansion (Bottom, scanned)
File:Vortex Memory Expansion Advert (CPC Schneider International, issue 8-1985, page 15).jpg|Advert (CPCI 8-1985)
Image:Leaftlet Front.jpg|SP64 The 520 Concept Leaftlet Front
Image:Leaftlet Inside.jpg|SP64 The 520 Concept Leaftlet Inside
Image:Letter 30-1-86.jpg|Screens Microcomputer Distribution Letter - 30/01/1986
</gallery>
* [[Media:BOS10ALT.ZIP]] - BOS v1.0 ROM-image (Alternative version)
* [[Media:Bos21.zip]] - BOS v2.1 ROM-image
* [[Media:BOS21 664.zip]] BOS v2.1 ROM-image (CPC 664 version)
* [[media:vramid.zip|Vortex RAM ID ROM]] - RAM ID ROM Image
== Weblinks ==
* [http://www.cpctech.org.uk/docs/sp512.html Vortex SP512 RAM Card]
[[Category:Peripherals]] [[Category:Manual]][[Category:Memory expansions]][[Category:Expansion ROM]]
