What does high ratio of functionality to I/O mean ?

what does this mean please, i read it online:

Asics are best suited to applications with relatively high ratio of functionality to input/output. PALs are more suited to systems with low functionality and high pin-out.

i need to know what does functionality to I/O mean ???
and what is the reason behind this info technically

thanks,
Salma

Re: ASICs and PALs

Hi salma. I'll try to answer your question to some extent.
Well functionality of ASICs is the extent of programmability, that is how best you can use it, how various applications are carried out by the ASIC.
And the ratio of functionality to i/o is the specification that suggests maximum number of programmability you can get with least number of inputs. This is due to ASICs are meant for specific applications and their efficiency is based on the applications they perform with least inputs available (that is low pin outs)

As contrary to the above fact, PALs are just the arrays of logics which have large number of inputs and outputs (pin outs) But their functionality is still resitricted. they could not perform multiple functions as is the case with ASIC.

I hope you are not completely lost after that explanation!..

Re: ASICs and PALs

salma ali bakr said:

what does functionality to I/O mean ???

Click to expand...

A "high ratio of functionality to i/o" means that the application has LOTS of internal logic circuitry as compared to its number of i/o's. For example, consider a hypothetical application which performs real time fft conversions and has only the following i/o's:

* input: clock.
* input: serialized data stream from an a/d converter.
* input: adc frame marker.
* output: serialized fft output data.
* output: fft frame marker.

This application requires a bunch of mac units operating in parallel, along with serializer, deserializer and various other state machines. How many equivalent gates might that require? 100,000 or more? But it has only 5 i/o's! So this application might be a good fit for an asic because it has a large amount of internal logic compared to its i/o count.

Contrast the above device with a pal, which might have 20 i/o pins but substantially less internal logic than you would find in a typical asic. To implement the above application with pals might require hundreds of pal devices because each pal has a relatively small ratio of functionality (internal logic) to i/o count.