Picaxe 40x2

steliosm

Senior Member
Hello all.
I'm considering using a 40x2 chip for a project I'm working on. I'm going through the datasheet to have a better understanding of the chp's internals. What is not clear to me at the moment, is how I am supposed to connect the power to the chip. I see it has dual +V, 0V pins (44x2 SMD version) and I can find circuits using the PIC18F45K22 either having both +V/0V pins connected or using just one of the pairs. Is there a reason for selecting one over the other?
 

inglewoodpete

Senior Member
The power pins do connect together internally but it has low current carrying capability. Always best to have good connections from both sets of pins to Vdd and ground, WITH 100n decoupling at both sets of pins. Absolutely essential if running at higher clock speeds.
 

inglewoodpete

Senior Member
Electrical noise on the power rails comes from two areas: any switching components around the PIC/PICAXE (inductors/relays/motors are the worst offenders) and inside the PIC/PICAXE, where there is a constant cacophony of switching noise. In some circumstances, switching noise generated within the chip can affect the chip's performance, especially at their higher operating speeds. Decoupling caps mounted close to the chip's pins help to minimise the impact of the noise.

One of the best decoupling configurations I've seen on a microcontroller is in the attached photo. I usually use through-hole components, though.
DecouplingCap.jpg
 

steliosm

Senior Member
So I guess, that would mean 2 decoupling capacitors next to the power lines. It does like it was added at the last time in the pictures :)
 
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