HSEROUT problem at 20MHz

[manxman]

Problem has been completely solved, as you suggested, by putting 0.1uF ceramic caps spanning the power supply lines to the PIC and the MAX232 on my breadboard. Thanks for the solution.

Incidentally, I found another problem relating to power supplies when experimenting with the 16F877. Like many PICs, the device has 2 pins (on opposite sides of the DIP) for each of the VDD and VSS connections. Thinking it would be good to connect up both sets, I found the PIC drew a heavy current and did'nt work. Only one pair should be used. The datasheet does not detail this.

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In electronics there is no such thing as a new idea, only new applications of old ideas.

[keithdoxey]

Incidentally, I found another problem relating to power supplies when experimenting with the 16F877. Like many PICs, the device has 2 pins (on opposite sides of the DIP) for each of the VDD and VSS connections. Thinking it would be good to connect up both sets, I found the PIC drew a heavy current and did'nt work. Only one pair should be used. The datasheet does not detail this.

Many of the larger PICs have multiple power pins.

ALL OF THESE SHOULD BE CONNECTED.

They are not duplicated to make PCB layout easier, they are there to feed power to all parts of the chip without burning out internal tracks. IF you only use one set you will eventually damage a PIC and could also have eratic behaviour of your program.

I would respectfully suggest that the reason your PIC drew a heavy current and didnt work was due to inadvetantly shorting out the power supply as the two sets of pins are NOT exactly opposite but slightly offset making a wiring error a distinct possibility particularly when breadboarding a design.