Debugging the debugger: B3 pic18LF Vdd below 3.0volt problem

Torello · Joined: 29 Sep 2006 Posts: 120

Hello,

Using the the 18LF4620 on 3 volt in combination with the ICD. I can debug and use the monitor above Vdd>3.1 volt. When it becomes 3.0 the communication starts to stumble and at 2.9 it stops. Looking at the scope B3 is still generating serial data. So the ICD running at 5 volt from the USB has an interface problem (hi level of 3v digital signal is not hi enough for the 5volt powered ICD)

Is there a simple solution for this?

Kind regards,
Edwin.

Torello · Joined: 29 Sep 2006 Posts: 120

"Quick and dirty solution" (i've got no time to wait)

Open the device. Search for the pullup (10k) to Vdd target on the B3 line and search for the serial resistor (330R).
Remove them both. Put a Bat82 in place of the serial resistor kathode to target connector. Pull the other side to 5v usb with a serie resistor of 4k7. You can connect the other side of the resistor to p20 of the 18F252soic for example.

If B3 is also used as output (what I did not see yet) then problems will arise. For now I can monitor my target running even below 3volt.

succes..