Current levels on joystick port

[patrickm]

Hi,

While making my own controller, I decided to measure the current levels on the joystick port.

For joy0, joy1, joy2 and the fire button, I measure between 0.8mA to 0.9mA when connected to ground. But for joy3, I measure 3.1mA, which is significantly more.

Does anyone know what reasonable values should be? Could this be a sign that something is failing?

[Mike]

Joy3 has a dedicated connection to the other 6522 VIA, on port B. Port B is capable of sourcing more current, and normally, this pin also is set to output. Joystick routines temporarily do a POKE37154,127 to make this an input pin and then a POKE37154,255 to restore to default, otherwise the keyboard scan does not work correctly.

You could try POKE37154,127 in direct mode to see if this reduces the current. With STOP/RESTORE you can reinit the register.

[patrickm]

Thanks. The poke did the trick.

The measured current is now much closer to the others at 0.95mA.

[Mike]

Nice!

BTW, we discussed the current sourcing/sinking capability of VIA port B some time ago here in Denial when it was used to operate a 4 bit D/A-converter, see here: User port sound.

Here's the relevant schematic in the data sheet:



Note the switching FET to the left of the pull-up FET.