"Laurens Holst" <[EMAIL PROTECTED]> wrote:
> >Yes, and why not 7.16MHz MSX1? BTW, how does a 7.16MHz works? I didn't
> >change the main clock of my MSX2 because I know that V9938 won't work.
>
> When accessing the I/O-ports (there's a pin on the Z80 which indicates it)
> the board switches the processor back to 3.5 MHz... Later, 'smart'
> 7MHz-boards (called Advanced 7MHz) appeared, which only switched back to
> 3.5MHz when there was VDP I/O. This way, SCSI, Memory, MoonSound etc. I/O is
> all done at maximum speed.
>
> I'd like to have the last one too (or better: 10MHz!) but I don't know where
> to get it...
If you have 7 MHz., you have it!
There's no different boards or ciruits here (well...mine and 7 MHz.
are different!). The turbo circuit (mine OR any 7 MHz.) just runs at
high speed, until it is signalled to step back to 3.58 MHz.
For this signalling it has a number of inputs, that you can connect
to signals, that are activated for parts that can't run on high
speed.
Usually, there are only 2 connections here: a manual switch, and the
Z80's IORQ-signal. That way, it runs on high speed, until (manual
switch used) or (access to ANY I/O port).
This "smart/advanced" as Laurens calls it, is just other connection:
IORQ signal removed, but replaced with VDP's IORD and IOWR signals.
That way, instead of for ANY I/O port, it is switched back only for
access to VDP ports.
You can connect any other signal here: floppycontroller or diskROM
chipselect for slowing on diskaccess, some ROM chipselect, if it's a
slow ROM not suitable for 7 MHz., chipselect of internal MSX-Music,
etc. etc.
Using this construction can be faster, but in practice, the
difference you notice is small, and many disadvantages:
-You have to connected a signal for every single piece of hardware
that requires 3.58 MHz. access: VDP, MSX Audio, MSX-Music, diskaccess
(sometimes), Gouda's SCSI interface, etc. etc. etc.
"Slower" construction is only 1 signal (Z80's IORQ)
-Every cartridge you use that doesn't work on turbo, has to feed this
switch-back signal back to the computer somehow. For example, if you
have MSX-Music cartridge, you would have to switch back for
chipselect of MSX-Music IC. But: this is not in the computer, only
inside the cartridge! Most practical solution is to put this signal
in the cartridge on a reserved cartridge-slot pin, and connect this
cartridge-slot pin in the computer with the turbo circuit. That's a
big hastle, modifying a bunch of cartridges this way, and: only for
use on a particular machine!
-Sound cartridges usually still won't sound right on turbo, untill
they have their own internal 3.58 MHz. clock added.
And you might think all is working, but find out later, that yet
another piece of hardware doesn't quite do it on turbo. Or not
anymore, if you add another MHz. to the turbo clock speed.
Examples: the mouse, HD interfaces, fast diskROMs, etc. etc.
Why have this much trouble, for so little gain?
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx MSX Tech Doc page
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put
in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the
quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
