Bernhard Kuhn wrote:
> DoC is a funny thing: i was wondering how it could work and came quickly
> to
> to the point that it has to use some kind of bank switching
> (I did�t had time to look into thier driver code). But AFAIK, the DoCs
> have
> only a 8KByte window and i had no idea what is the default state
> and how to reprogram this beast ... so i decided to do
> something similar on my own, using the full 256KByte address range.
>
> But now, i am not sure any more if this was realy a good idea, because:
>
> 1) DoCs can be bought directly from stock (it�s not easy to get 29F040
> DIL)
> 2) DoCs can be much bigger than the 4 MByte of the Flash Extender
> 3) DoCs are physicaly much smaller than the Flash Extender
> 4) with it�s 8Kbyte window limit, DoCs can be used for a wide range
> of mainbords
> 5) The necessary "Daughterboard" to switch between factory default
> flash and DoC could be kept absolutly simple without any additional
> chips (all relevant pins are just connected in parallel, except the
> chip-select signals)
>
The other issues involved with making a daughtercard as idiot proof as possible are
operating and
programming voltages.
3 VCC with 3 VPP, 3 VCC with 5 VPP, 5 VCC with 5 VPP, 5 VCC with 12 VPP for factory
Flash BIOS and
versions of the DOC in 3 VCC with 3 VPP and 5 VCC with 5 VPP.
Physical size is also a concern. Lots of the mother boards I've used have the Flash
BIOS device
located in a very congested area of the board due to very poor design of the pcb
layout. I've
actually had some Flash BIOS devices that conflicted with the mechanical space for PCI
or ISA cards
and had to leave a slot open due to this. I could make two boards one with the card
parallel to the
motherboard and another that would be at a right angle to the motherboard.
>
> But there are also disadvantages:
> 1) M-Systems is realy concerned about their "Intellectual Property"
> (laughing)
> 2) Does there exist official programming information? (specs)
>
Programming information for the DOC is available off the M-Systems site.
The reasons many designs go with M-Systems DOC is that it comes in a small package and
the drivers
and interface are made pretty simple to design in. The M-Systems Flash File System and
the drivers
can make the devices look like many Megs of memory paged through an 8K window or as a
hard drive
with all the flash programming routines and wear leveling kept transparent from the
user. It makes
sense when they consider the design costs and effort of doing it all if they don't
have the in house
design talent especially if they need to treat the DOC as a drive where it's going to
be written to
many times. If the DOC is going to be just used like a ROM and only be read from and
possibly only
be written to for BIOS updates then -IMHO- if you have the talent and you're going
into volume the
DOC's are a bit expensive unless you can get a deal on pricing.
Bari
