SeanH
- 9th September 2004, 12:03
Hi
I am using a 12F629 chip for a project and got a strange problem.
I am using GPIO.0 and GPIO.2 connected to a FTDI USB>RS232 converter chip.
The transmit is conected to GPIO.0 and receive connected to GPIO.2 pin, these pins USB side idle high.
Placing a meter on these two pins they read 3.3V with or without 12F629 in circuit.
I am using GPIO.3 as a Input (Internal MCLR being used) that monitors a button and gets driven high when pressed, External 20 mhz xtal and VDD is supplied via a SP switch.
If the unit is turned on and the button is held down then the chip will jump to a routine.
Now with the switch off I would expect the Chips VDD input to be 0Volts but it is actually 3.3Volts and the chip will never reset. If I place a double pole switch in and isolate the GND and VDD then obviously it works.
How come the Chip is drawing Power from these pins and keeping the Chip running without the VDD line having any supply????
I popped a 18F252 chip in it's place and tried it on the RB ports and when the SP switch was turned off it did indeed power down the chip and the 3.3V on the RB pins did not supply power to the chip.
Just curious on any reason why this happens with the 12F629 chips?
Regards
Sean.
I am using a 12F629 chip for a project and got a strange problem.
I am using GPIO.0 and GPIO.2 connected to a FTDI USB>RS232 converter chip.
The transmit is conected to GPIO.0 and receive connected to GPIO.2 pin, these pins USB side idle high.
Placing a meter on these two pins they read 3.3V with or without 12F629 in circuit.
I am using GPIO.3 as a Input (Internal MCLR being used) that monitors a button and gets driven high when pressed, External 20 mhz xtal and VDD is supplied via a SP switch.
If the unit is turned on and the button is held down then the chip will jump to a routine.
Now with the switch off I would expect the Chips VDD input to be 0Volts but it is actually 3.3Volts and the chip will never reset. If I place a double pole switch in and isolate the GND and VDD then obviously it works.
How come the Chip is drawing Power from these pins and keeping the Chip running without the VDD line having any supply????
I popped a 18F252 chip in it's place and tried it on the RB ports and when the SP switch was turned off it did indeed power down the chip and the 3.3V on the RB pins did not supply power to the chip.
Just curious on any reason why this happens with the 12F629 chips?
Regards
Sean.