pld macrocell usage

Feb 24, 2005 2 Replies
M

I am designing usin an xc9500 Xilinx PLD and i observed some strange behavior, wondering if anyone can confirm or deny.



It appears that a macrocell is used for each output pin (or bidirectional). I get a summery like this:



Total Macrocells Available 216 Registered Macrocells 124 Non-registered Macrocells driving I/O 48


My design has about 120 macrocells, and these 48 dirving are bothering me. Why does it need a macrocell for the I/O. I put the chip in low power output mode, hoping that would free them up, but no luck.


Mike D



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V

I think beyond this 48 pins you have other pins that are driven by registed macrocells too.

I read the XC9500 user manual and I think it is designed so that you need one macrocell for each output pin.

vax, 9000

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F

"vax, 9000" schrieb im Newsbeitrag news:cvlkvg$64i$ snipped-for-privacy@charm.magnus.acs.ohio-state.edu...

Exactly. With the coolrunners, there is an option to use IO and macrocell independend, but I wouldnt base my design too much on it. Use a bigger CPLD or FPGA.

Regards Falk

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