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Altera_Forum's avatar
Altera_Forum
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17 years ago

Can a bidirectional port becomes both input and output at the same time?

I would like to create VHDL codes which are able to display data to the Input/Output port as well as receiving values of the port, if there is any changes to the port. Firstly, is it possible without...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
17 years ago

I also didn't understand exactly, what you want to achieve. Clearly, while a bidirectional port is driving out, either high or low, there shouldn't be a second driver at the node, that is driving the opposite level. Otherwise, the involved outputs can be damaged, at least when using higher drive strengths. Also the read back input level would be unpredictable.

A wired or circuit of several open drain outputs and a pullup resistor (as used with I2C bus or the smart card IO node) is a possible way to send and receive at the same time.