HELP ME about EP2C20Q240C8,PLEASE!

[Altera_Forum]

HI ALL 

I'm using the cycloneII(EP2C20Q240C8).I want to know what the difference the pin 178 and the others.when i use the pin 178 as LVTTL output,it cannot output a wave (frequency about 25MHz when i use crystal about 50Mhz),but when i use other pin,they can do it.why??? THE wave mentioned above is that i see by the signal-tap. what can i do to solve it?

[Altera_Forum]

Pin 178 can be either normal IO or the output of a pll: PLL2_OUTn. Are you driving this pin from logic (e.g as the output of a divider) or directly from the pll? In the latter case it doesn't work: see page 20 of "Pin Information for the Cyclone® II EP2C15A, EP2C20 and EP2C20A Devices.pdf" (http://www.altera.com/literature/dp/cyclone2/ep2c20_ep2c15a_ep2c20a.pdf).

[Altera_Forum]

no,we just use it as normal IO,as the ADC's control clock,frequency about 25MHz .when we use other IO,it can work well,but when we use then pin178,it cannot output the right wave. i'm so confused!

[Altera_Forum]

There should be no reason why pin 178 wouldn't function as you want it to. 

I suspect you have a either a short between pin 178 and ground, or you are not looking at the right pin (because of a routing swap or so), or because in the logic project the signal is not placed on that pin.

[Altera_Forum]

thank you for your answer,but i have tried in two pcb.the first doubt can be excluded. the second doubt: i check the pin many times. 

but i have done another experiment, i use the pin178 to output other slow signal, it can do it.so??????

[Altera_Forum]

The reason must then be searched in the logic. If you say that pin 178 outputs a 'slow' signal, how slow is this then? I suggest you make a small project that only drives this pin as the output of a counter? In fact this morning I did make such a small project to simulate to some extent what you are doing, so I just add the .qar for your perusal.

[Altera_Forum]

thank you for your hard work again! 

the attachments is my code, can you find some errors for me???thanks a lot!! the ad_clk is assigned to the pin178.

[Altera_Forum]

I did a quick compile/simulate on your file and see no reason why the signal does not appear on pin 178. I attach the .qar for your perusal.

[Altera_Forum]

I also didn't find out any problem by simulation, but when i use the signal-tap to watch the ad_clk on the pin178 i find that the program became wrong. The right output wave is like the attachment. 

Two years ago, my another colleague also find some problem when he used the EP2C20Q240C8 in other project.he also solved the problem by swapping the pin.

[Altera_Forum]

You didn't say a word about SignalTap in your original post! Did you check at all, if the pin is working correct without connecting SignalTap logic to it? If so, it's a completely different topic in my opinion.

[Altera_Forum]

you mean the signal tap is unbelieveable?? i will have a try next week. thanks!

[Altera_Forum]

no! i tried the code without the signal tap,and it still didn't work. i also found the chip become very hot. So i have decided to give up use the pin178.

[Altera_Forum]

--- Quote Start ---  i also found the chip become very hot  --- Quote End ---  That's actually alarming. I don't think, that it happens because you're using a particular pin as output. As a more likely reason, you may have shorted a pin that is driven as output (e.g. an unused pin) or the device is simply damaged.    --- Quote Start ---  you mean the signal tap is unbelieveable  --- Quote End ---  I mean, that some pins may be unaccesible for SignalTap by it's nature. SignalTap uses existing IO buffers and registers. If these resources don't exist for a particular pin, SignalTap can't work. There are some cases, where SignalTap can't access a pin (e.g. withh DDIO function) or doesn't necessarily reflect the pin state correctly (e.g. input function of bidirectional pins, but only in some cases, depending on other design parameters). I would expect problems also with dedicated clock outputs, but I'm not sure about.

[Altera_Forum]

i use altera fpga many years, i will not let the pin be shorted. the unused pin were made as input tri_stated.But when i didn't use the pin178, the chip is normally cool.Meanwhile i have tried two pcb board to test, the result is same.

[Altera_Forum]

I'm not aware of a known issue with pin 178 of the said Cyclone II chip, if I understand right, you have reported, that it had worked for you in other designs too. So there are two possible explanations: 

- A hidden short on your PCB - A Quartus or Cyclone II silicone bug In the latter case, you should contact Altera suport with an example design, that reproduces the problem.