On Monday 28 August 2006 01:40, Jack Carroll wrote: > On Sat, Aug 26, 2006 at 02:53:57AM +0100, Peter TB Brett wrote: > > Having said that, chaining onto the end of the SPI bus is the most > > reasonable solution I've heard so far. I'd suggest a PIC + serial port > > as the tidiest solution, requiring the following components: > > That's one of the higher-capability tools you could hang on the SPI > bus. I suggested a 68HC908AB32, but there are PICs that would work too. > Depending on the raw hooks in the ASIC, you could use that to set the > boot-time video mode, simulate an off-board EEPROM that substitutes itself > for the on-board EEPROM, write a real off-board EEPROM, write to the > on-board EEPROM, or if the on-chip logic to support it is affordable, > provide an TRV10 debugger interface through its RS-232 port.
That was the general idea. I'd go for a PIC -- the 16F87 is one that supports
both RS232 & SPI directly, for example. The advantage is, it's cheap and
requires very few external components.
> An SPI tool that sets the video mode on power-up and does nothing
> else could be a lot simpler. All it needs is about 120 DIP switches and a
> shift register chain to read them in.
Yeah, I saw this discussion, but as I mentioned I was thinking of a tool that
would be more useful for programming/test/repair purposes at the factory or
vendor. Also, the PIC-based cable could well be smaller and easier to use.
The kind of usage I envisaged for the PIC-based cable was as follows. Using
your old video card, you boot up and use a nice command-line/curses-based/GUI
wizard to program the cable with the desired settings. You then turn off
your computer, replace your video card and plug in the cable, and boot up
again. This makes the process a little more fool-proof and probably quicker
than messing about with hundreds of fiddly little DIP-switches, IMHO.
Pricing for USB version (UK prices, based on Farnell/Digikey):
- PIC16F87 £2.50-ish
- FT232 £2.26
(strangely, MAX233 serial line drivers seem to be extraordinarily highly
priced at £5+)
- USB A R/A connector £0.30
- Some 5-core cable £0.25 per metre approx.
- Some discrete resistors/capacitors
- A connector to plug onto the card
- A PCB
It'll also need some diodes, since it's going to be USB-powered during setup
and card-powered during reading.
DIL switches seem to be cheapest at about £1+ for 4, making the switch-based
tool at least £30 for switches alone. Then you've got the facts that (a)
it'll take a bunch more chips for the shift register, and (b) you'll need a
much larger PCB.
Peter
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