Re: CPLD input question (by a primary user from china)

Altera_Forum · ‎07-15-2008

HI,Guys,I'm debuging EMP240T100。

I have set a signal "DONE" as input,and the pin doesn't connected to any device,but when I read it by DATA_BUS,it is '1',

ps:DATA_BUS is a 16bits data bus which is defined as input/output。

The codes are as follows:

DATA_BUS<="00000000000" & PRO & INI & DONE & CLK & DA when (RE='0')

the problem has puzzled me for days,can anybody tell me why?

thank you in advance!

Altera_Forum · ‎09-26-2008

Is 'Done' an input pin of the device? In that case, can you check if you have specified it correctly in the pin-options? And if it is a signal, then has there been any driver to that?

Altera_Forum · ‎10-08-2008

--- Quote Start ---

Is 'Done' an input pin of the device? In that case, can you check if you have specified it correctly in the pin-options? And if it is a signal, then has there been any driver to that?

--- Quote End ---

'Done' is just an input signal of the cpld,which is drivered by fpga.

that's all.

I haven't solve it yet.

thanks for your reply!

Altera_Forum · ‎10-08-2008

--- Quote Start ---

'Done' is just an input signal of the cpld,which is drivered by fpga.

that's all.

I haven't solve it yet.

thanks for your reply!

--- Quote End ---

That means 'Done' has a driver (as it is driven by an FPGA driver). Can you write about the following to make your query clearer:

1. Where are you observing 'Done' as '1': On an oscilloscope/logic analyzer or is it a simulation? If you are observing this on oscilloscope then clearly since the pin is driven by an FPGA, you are bound to see '1' or '0' or whatever it has been driven. If it is a simulation, and 'Done' is an input port then you will see only that value at 'Done' which you assign in your testbench.

2. You said Databus can be an "input/output". Do you mean it is an inout port? If yes then isn't it possible that it can be a source too rathen than just a sink?