From: charlieDOTd@verEYEzon.net   
      
   On 8/31/2022 6:08 PM, Anthony Ortiz wrote:   
   > So I've been fooling around with my fpga on a peripheral card doing reads   
   and writes to the bus, trying to get the timing just right, but it's such a   
   pain to power off the apple ii, remove the peripheral card, plug in the usb   
   cord to the fpga, flash    
   the new vhdl update, unplug usb cord, put the card back in the slot and power   
   up the apple II again, ad nauseum. To simplify things I decided to use an   
   external usb power with an on/off switch and plug the usb cord into that and   
   leave the cord plugged    
   into the fpga while it's in the apple ii slot. I have to make sure to have   
   either the usb port or the apple ii off when the other's on, or else there'll   
   be a lot of smoke.   
   >   
   > As I finished flashing an update to the fpga card, I happened to glance at   
   my oscillosope which was connected to my fpga and I saw it generating a wave   
   form, a 1mhz signal that can only be generated if phase0 was actively feeding   
   it, but the apple II    
   was off! I was scratching my head... Surely the motherboard clock can't still   
   be working with the apple ii powered off, can it? So I unplugged the power   
   cord from the apple ii and... the waveform was still there! At that moment I   
   realized that the USB    
   powering the fpga was also feeding power to the apple ii via the 5v line, and   
   that must be powering the clock. It must also be powering the ROM (and maybe   
   RAM?) because I was able to read from it just fine.   
   >   
   > I wanted to ask you guys out there in the know... is this okay or am I at   
   risk of damaging something? Assuming it's okay, can I rely on debugging it   
   this way with the apple ii power off, or will the timing be different with the   
   apple II on thus making    
   any debugging while off pointless?   
   >   
   > Many thanks in advance.   
   >   
   > Anthony   
      
   I don't know if it is okay or not but it got me curious so I got out my   
   old scope and tried to replicate what you are doing only with my Carte   
   Blanche II card.   
      
   I first connected my probe to phase0 pin of the Apple IIgs slot and to   
   ground on the slot.  I then removed my USB connection to the Carte   
   Blanche II.   
      
   Powered up the IIgs and got a wave with some ringing but less than what   
   I see in your pictures (my scope is an old analog scope).   
      
   Turned off the IIgs.  No signal on scope.   
   Plugged in USB.  Still no signal on scope.   
   Tried programming the Carte Blanche II.  It won't program without the   
   IIgs power on and still no signal on scope.   
      
   For what it is worth.  I leave my USB connected all the time and program   
   the FPGA or Flash the non-volatile memory over and over without turning   
   anything on/off.   
      
   Is your USB connection to a USB chip on your board or is it a USB to   
   JTAG cable?   
      
   Charlie   
      
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