Stupid simple question.....

[chien_fu]

I really hate this stuff.... it makes me want to stab myself in the eyeball with a fork.

I'm measuring 3v from Pin1 (GP1) on my 12F683.
I'm using a 3v coin cell. It measures 3v.
I connect a LED to Pin1, it lights.
YAY! Next frickin challenge....

I connect a small vibe motor to my 3v battery, it vibrates like crazy. Yay.
I connect my small vibe motor to Pin1 (measuring 3v) It does absolutely nothing.
I connect the LED to Pin1.. it lights..
I connect the motor to Pin1 ... it does nothing
I punch stuff... that doesn't help.

I don't know what else to try...
The vibe motor draws about 35-40mA

I see that the IO pins supply 25 mA but the GPIO can supply 90mA...
What's the difference?

[ScaleRobotics]

The vibe motor draws about 35-40mA

I see that the IO pins supply 25 mA but the GPIO can supply 90mA...
What's the difference?

A single pin can put out a max of 25mA, but the entire GPIO (all output pins) can put out a max of 90mA. You could use a transistor, or you could have two pins control the motor (and hope start current would not be too high).

[chien_fu]

So I tried driving it with two pins but something else is screwy now....

This is what I have:

OUTPUT Pin1
output Pin2

Startup:

for startupalarm = 1 to 4
high 2 
high 1 
pause 5000
low 2 
low 1 
pause 5000
next startupalarm

It seems that "high 2" does not actually switch the pin high, but just ticks it high for a split second. "high 1" switches the pin high and it is held high for 5 seconds until it is switched low...

This is the same regardless of which pins I use. The line of code immediately preceding the pause command works, all others do not. Nothing else is connected to the chip, it's all by itself on a breadboard.............

[HenrikOlsson]

Hi,
You're suffering from what is called a RMW problem (read-modify-write). The way the PIC works when setting a single bit in a register, like the GPIO-port in this case, is to first read the whole register, then set the bit in question and finally writing the whole register "back".

Because your motor presents a large a load to the pin (especially at startup) the voltage on the pin will sag or be low. So what is happening is this:
First you have the High 2. This reads the port (as a byte), sets bit 2 and writes the whole byte back to the port.
Now you have High 1 which does the same thing but because pin2 is heavily loaded it will read as 0 when the port is read, the PIC then sets bit1 and write back to the port resulting in bit 2 now being reset to 0.

The best bet is to use a transistor to drive the motor. If that's not an option then write to the port directly, setting both pins at the same time. You do this in the same way as Darrel showed you how to write to CMCON etc - look up the physical adress of GPIO and use POKE to write to it.

[Melanie]

Remember also, you must treat your Motor as an INDUCTOR or RELAY. The back emf could destroy your PIC pin or Transistor switching it. Put that all important Diode reverse-biased across the Motor.

[Acetronics2]

+1 .....

Good answer from Henrik ...

[HenrikOlsson]

Nah, if you look at section 9.1 of the mid-range manual you'll find the following:

All write operations (such as BSF and BCF instructions) are read-modify-write operations. Therefore a write to a port implies that the port pins are read, this value is modified, and then written to the port data latch.

So I'll stick to my theory ;-)