CPLD MaxII, pull up resistor and led

[Altera_Forum]

Hello 

 I have to drive 26 Leds through the CPLD MaxII.   I have seen that this CPLD have internal pull up resistor that can be enable or not and apparently we can choose their value.  My question is: can we use those resistor for current limitation?

[Altera_Forum]

--- Quote Start ---  apparently we can choose their value  --- Quote End ---   No, they are fixed. Output drive strength can be selected low or high. But you'll normally need external current limiting resistors to set the current of connected LEDs.

[Altera_Forum]

Ok thanks.  

 So have you any idea to avoid the use of 26 resistors?  I think about implementing a led driver in the CPLD but I'm not sure that it will decrease my number of resistor.

[Altera_Forum]

If you don't need high average LED currents, multiplexing the LEDs in a matrix can save output pins and resistors. Using common chip resistor arrays, 26 shouldn't be a problem, however.

[Altera_Forum]

The maximum forward current is 50ma. I will use PWM to drive the LED. 

 Do you think it is ok for multiplexing.   I don't know what is multiplexing and how to do that in the CPLD, I am a begginer. I will check that (but if you want or have time to explain feel free :)).  The other proof that I am a begginer, is that I didn't know what was a common chip resistor (I've already check).  Thanks for your help

[Altera_Forum]

You should also check a respective application note http://www.altera.com/literature/an/an286.pdf 

 The maximum pin current is specified with 25 mA.  Chip resistor array like http://www.farnell.com/datasheets/467947.pdf