quick question, interfacing 2 CPLD's together....

[Buriedcode]

Hi, I've got 2 64 MC CPLD's, and I would like to be able to create designs for 128 macrocell devices. Assuming I can easily partition a design to fit on two chips, is there any special way I should 'physically'(or electrically) connect them? I mean, is it OK to simply connect, say, 8 I/O's from one to the other, assuming actual Inputs and Outputs are configured correctly? You see I'm designing a dev. board for these CPLD's and I don't want to order the PCB only to find out that I require a buffer or something. So, basically, is it ok to directly connect an I/O from one chip the I/O of another? Both chips being identical (MACH4A5-64/32)

It seems like a silly question, because Microcontrollers don't mind it, but I've had a couple of CPLD's that heated up quite badly when I connected them together.

Thanks

Buried(in)Code

 

[cyr]

As long as you actually connect outputs to inputs and not two outputs driving different levels there's no problem.

You could always have series resistors (100-1000 ohm or so) to limit the current in case you mess up and place outputs on the wrong pins.

 

[Buriedcode]

Hi cyr, thanks for your reply!

Series resistors for currebt limiting probably would be a good idea, because I'm bound to set up the I/O's wrong at some point I'll add them to my design, thank god for SMT resistor networks

Thanks again man,

BuriedCode.