What is the normal state of the input ports

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BritishCat
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What is the normal state of the input ports

Post by BritishCat »

Hello. May I ask an one question? I Didn't see anywhere a clear description about it. What is the default state of the input ports? For example I defined 4 bit port XU208 as the input, and I going to change the states of the bits using jumpers. How can I do it? I read in describtions about the internal pullup and pulldwn resistors. How can I assign them to the input port? Are there an opportunity to use them?


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fabriceo
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Post by fabriceo »

Hi,
you have to use the builtin function (xs1.h)
void peek(void port p);
to read the port value (direct voltage on the pins)

to enable pull_up/down you have to use
void set_port_pull_up(void port p);
void set_port_pull_down(void port p);

but each have the side effect to configure the port in drive low or drive high respectively, so be sure that the port is set to all 0 or 1 before.

so a sequence like this to read the button, IF they are connected to GND should be ok

Code: Select all

myport <: 0; set_port_pull_up(myport);
unsigned old, buttons;
while (1) {
   buttons = peek(myport);
   if (buttons != old) printf("buttons=0x%X\n");
   old = buttons; }
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BritishCat
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Post by BritishCat »

Thank You. I've got it!
Joe
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Post by Joe »

No need to use peek if it's an input only port.

on tile[0]: in port p_but = XS1_PORT_4E;

unsigned input_but_val;
p_but :> input_but_val;

The default is to have no pullup or pulldown. If you want to enable the weak internal pullup or pulldown then you can use the function as fabriceo says:

set_port_pull_up(p_but);
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BritishCat
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Post by BritishCat »

Thank you. I've understood where I can find it (xs1.h)