>        the 6 LEDs utilizing a common pin on one side. Something like:
>
>         Port pin---+-[220ohm]--+---[LED]------  Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin
>                    |
>                    +-[220ohm]--+---[LED]------- Port pin

Hi,

   the problem with this design arises when you want all four LEDs running.
If we allow for 10mA through each LED the common pin has to source and sink
40mA. According to the 16C5X data sheet in front of me the specification is
sink 25mA and source 20mA. In addition to which there are limits on total
currents for each port, and for the total device.

One way around this is to use the common pin to drive a pair of transistors
but that increases the part count and we are still faced with a 40mA per
port limitation. Perhaps someone has a better solution.

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail:      kdowsett@rpms.ac.uk
Phone:       0181-740-3162
Fax:         0181-743-3987

Snail mail:  MRC Clinical Sciences Centre, Cyclotron Unit.
                 Hammersmith Hospital. London W12 0NN.