PC Engine expansion port

[duo_r]

ok so two things, first on the 101 PC Engine secrets page it says 13 pins were unused. Were these the video bus lines? if so which ones (since there are 15 apparently).

Also 2nd - for PC Engine shuttle it says the only thing preventing it from using a CD-ROM accessory is the IRQ2 pin. If this pin were added in, is that all it would take for a Shuttle to work with a CD-Rom? Has this been tested at all?

[NFG]

On the first point, yes, these are the video bus lines.  The Secrets page is quite a bit older than the latest expansion pinout.

On the second, probably not?  Give it a go and report back.  =D

[duo_r]

I have made an adapter and have a wiring diagram created. Is there any risk to connecting some of these lines together? I can post my proposed wiring and maybe someone can spot check. I of course know it's always risky doing stuff like this but just wondering if certain data lines connect that shouldn't if it could be bad news for the CD Rom or Shuttle. 

[NFG]

I'd certainly like to see it.  On the connecting front, you should be fine to connect things like Vcc and GND (to Vcc and GND, not to each other!) 

A multimeter should help you, any points that beep can be combined.

[duo_r]

 
ok, so I just had an RAU-30 arrive and my theory is that whatever is needed to connect to a PCE and run a CD-ROM would be wired up. Upon initial inspection, I discovered 29 pins on the connector that are No Connect. So this is good news for the theory that the Shuttle can be connected to the expansion port if we add in the IRQ2. Here is a graph of what I found so far (not this is just based on an initial test).

All the pins shaded black with red lettering (and strikethrough) are no connect on RAU-30. Also another interesting find, the CDD pin on the RAU-30 is connected to ground. Perhaps that indicates the CDD is in fact connected when attached to a PCE.




In addition, here is my proposed wiring diagram (this is just an early revision). On the left (PCES) is the PC Engine shuttle pin, Desc - is the pin description and RAU is the pin # this will go to on the RAU-30. I discovered that /RST is not connected on RAU-30, if I find that the Shuttle Memory doesn't use RST, I may end up using this as IRQ2 which would be nice as no external modification would be necessary on the PCE Shuttle.

[NFG]

/CDD is almost certainly used, since it tells the PCE that a CD ROM is attached.

I doubt /RST is used by the backup RAM, since that pin is used to reset the console, and I honestly can't imagine why the backup unit would need to do that.  For that matter I don't know why the CDROM would either.  Hmm.

[duo_r]

Yes im going to check the backup RAM and see if RST is used.

One other question - the PC exp port has digital and analogue grounds. The Shuttle just has ground. What do the digital grounds?

[duo_r]

Also OE isnt in the PCE Exp port, so i wont worry about that.

[duo_r]

ok on the memory unit, A16 IS being used for the PCE Shuttle. So I can't use that unless I use a switch but I would really prefer not to install a switch on the shuttle. So now I am thinking of borrowing one of the ground pins in the shuttle and just making sure it is disconnected and can be designated as IRQ2.


Also Lawrence - thoughts on the digital ground VS analogue ground? Do I need to worry about that or is ground just ground?

[NFG]

I think the different grounds are to eliminate interference, but they still go to the same points eventually.  Use your multimeter to be sure. 

I'd try it and not worry about it, but I don't know the answer for certain.

[duo_r]

One side question:


the RST pin, when that pin is grounded that is what resets the system correct? Is this the equivalent to the RUN + Select reset?



http://www.gamesx.com/misctech/pcebp.php

[NFG]

Not quite the same, RUN+SELECT is a software feature, the game program has to watch for this and do something (which is why some games handle it differently).  The /RST pin forces the CPU to initiate its operations from a power-on state, whether it wants to or not.  But yes, that's what the pin does, it resets the machine.

[duo_r]

and to trigger the RST line it just has to go to ground obviously using a switch?

[duo_r]

Ok thats exactly how RST works, connect to ground and system resets. Also it takes slightly longer to reset compared to Run + Select.

[duo_r]

Here was my test button switch for RST line.