[ PC Engine (Core,Duo,etc...] How to get the RESET signal ? (for hardware mod)

[localheureux]

Hi,

All PCengine fans know how to work the Reset function (Run+Select on the pad) .... but how it really works inside the console ? (electronically..)

Would think that  sends a signal (surely a +5V ) somewhere to a pin of one of the chip, but which? (or other way?)
And is it possible to get this signal to add a real Reset button ?


Thanks for your help.

[Lawrence]

You can get the reset line from:

HuCard pin 36
Expansion connector B22
Hu6280 pin 11
Hu6270 pin 24

http://gamesx.com/wiki/doku.php?id=schematics:hu6270_netlist
http://gamesx.com/wiki/doku.php?id=schematics:hu6280_netlist

[localheureux]

Yeah-sss .... so quick and full reply, thanks a lot 

To be sure I understood, when I push Run+Select I can directly get the signal sent on the pin 36 of the Hucard player?
That's so simply? (by the way this is a +5V ?)

Thank you very much again 

[Lawrence]

I'm not sure what you're asking, 'get the signal'.

RUN+SELECT is a soft-reset.  The software may trigger a hard reset by pulling the /RESET line low, but I'm not sure.

[localheureux]

Oh excuse me, unfortunately my english is far to be perfect  


So... what exactly I need is a +5V to send only when we reset the console (it's why => my "to get the signal" ) .
But I think now I maybe understood, the best way should be to use the pin 11 on Hu6280.
"When Run and Select are pressed I suppose a +5V is "catchable" on the pin 11"

I'm right?  

[Lawrence]

Well, I can't be sure the software actually resets the machine or if it just resets the software when start&select are pressed.  Since the software reads the pad, it's free to do what it wants in this case.

Second, the slash before reset:  /reset   means it's ACTIVE LOW.  It is held high, with +5v, while the system is running.  When you want to reset it, you connect this pin to GROUND.

[l_oliveira]

The start+select thing is 100% soft reset.

On normal PCE units the hardware reset is used only once to start the unit. 

Going straight to the topic here: No, pushing Start + Select do not really reset the CPU. Games are coded to jump to the reset vector when the user press the key combo.

Some PCE games do not check for the reset key combo and it does not work after the CPU has crashed.

[localheureux]

Ok ....  thanks  guys I understand better  (I guess   )

But... (whatever is did all is hardware at the end, whatever I press on the pad all is "hardware" translated after).

Whatever was happened before (a software code sent to the CPU or any chip, or anything else soft or hard), when the console resest,  inevitably the  reset itself is hardware, that's inevitably due to a "hardware fonction" somewhere in the console (surely near or in the supply input), and this is surely due to a "signal" sent by a  hardware component to another hardware component who control the "reset event".
This is what I want to know.
Else  how to know how all of this work?

(Hope my english is good enough)


Thanks again guys

[l_oliveira]

To restart an simple  system like the PCE all you need to do is jump to the CPU reset vector.

On an MSX computer on MSX basic if you use the command "defusr0=0" and then use "a=usr(0)" the system will restart, because the CPU executes from address 0 when powered on or reset.

So on PCE an software instruction to jump to the reset vector address WILL RESTART THE GAME just in the same way as pressing an real physical reset button.  NO hardware reset is necessary for that.

[localheureux]

Ok I understand, thanks a lot.

There is no way to my request...