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Forum: FPGA, VHDL & Verilog Igloo Nano I/O tri-state buffer


Author: kamran q. (kamran_q)
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Hello,

I am using Igloo Nano AGLN030Z. I would like to know if igloo nano has 
Tri-State, input output buffers. I would really appreciate if some one 
points out the specific Block used for this purpose in Libero IDE. 
Looking forward.

Kamran.

: Moved by Moderator
Author: Lothar Miller (lkmiller) (Moderator)
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> I would like to know if igloo nano has Tri-State, input output buffers.
Even the simplest and oldest GAL has tristate buffers, so I would expect 
a much more recent technology having such buffers too.

But why not just searching the datasheet for "tristate"?

Author: kamran q. (kamran_q)
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Hello Lothar,
Yes I did.
I perhaps wasn't clear enough in my post.Let me explain.
I did find tristate buffers in the Datasheet, but I also want them to be 
bidirectional.
I have one controller talking to another controller via a cpld(igloo 
nano). Now in this basic communication I want following scenario:

1: Device one sets a register field to 1 to send data. Other device gets 
ready to read data.
2:Device 2 communicates with device one in the same way.
3:Other wise both show high impedance at output.

This all shall be done using only two I/O pins.

Kamran Qureshi.

Author: Lothar Miller (lkmiller) (Moderator)
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> I did find tristate buffers in the Datasheet, but I also want them
> to be bidirectional.
Thats usual behavior. In VHDL you write this and you will get a 
bidirectional buffer:
   portpin  <= signal_out when enable='1' else 'Z';
   signal_in <= portpin;

> 1: Device one sets a register field to 1 to send data.
>   Other device gets ready to read data.
> 2:Device 2 communicates with device one in the same way.
Hmhmhmmmmm...
This isn't very polished. How does this
> a register field
and
> This all shall be done using only two I/O pins.
fit together?

> This all shall be done using only two I/O pins.
Why not using a kind of RS232?

> 3: Other wise both show high impedance at output.
You always should/must have one driver (or at least a pullup/down 
resistor) on a tristate signal. Otherwise this signal can float and you 
will get a high current in both input stages.

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