Chip9$ input output on XIO ports - Cronologia

Renzo: /* Second experiment: write a gpio output (e.g. turn on/off a led diode) */

2015-10-10T11:11:57Z

Second experiment: write a gpio output (e.g. turn on/off a led diode)

Renzo: /* Second experiment: write a gpio output (e.g. turn on/off a led diode) */

2015-10-10T11:09:23Z

Second experiment: write a gpio output (e.g. turn on/off a led diode)

Renzo il 09:03, 10 ott 2015

2015-10-10T09:03:58Z

Renzo: Creata pagina con 'This tutorial shows how to read the value of a button or turn a led on and off. Chip9$ has a PCF8574A i2c port expander. It drives the ports named XIO-P0 to XIO-P7 (pin 13 to...'

2015-10-10T09:00:02Z

Creata pagina con 'This tutorial shows how to read the value of a button or turn a led on and off. Chip9$ has a PCF8574A i2c port expander. It drives the ports named XIO-P0 to XIO-P7 (pin 13 to...'

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This tutorial shows how to read the value of a button or turn a led on and off.

Chip9$ has a PCF8574A i2c port expander. It drives the ports named XIO-P0 to XIO-P7 (pin 13 to 20 on U14).

It is possible to use these ports from the shell command line.

<pre>
# cd /sys/class/gpio/
# ls
export gpiochip0 gpiochip408 unexport
</pre>

gpiochip408 is the PCF8574A expander. '''port numbered in the range 0-407 are GPIO of the AllWinner A13 SoC. Read carefully the manual and Chip schematics prior to use them'''.

The ports provided by the expander are the following:
<pre>
port export# pin
XIO-P0 408 13
XIO-P1 409 14
XIO-P2 410 15
XIO-P3 411 16
XIO-P4 412 17
XIO-P5 413 18
XIO-P6 414 19
XIO-P7 415 20
</pre>

=== First experiment: read a gpio input (e.g. a button) ===

Activate the XIO-P0 port:
# echo 408 > export
This generates a virtual dir gopio408:
# ls
export gpio408 gpiochip0 gpiochip408 unexport
# ls gpio408
active_low direction power uevent
device edge subsystem value
There is a pullup to the input:
# cat gpio408/value
1
Now, use a 10Kohm resistor to connect the pin 13 of U14 to ground (for example pin 1 of U14) (it works using a jumper, too. The resistor is for safety. It is more unlikely to damage the Chip toy.)
# cat gpio408/value
0
As you may guess, without the resistor or jumper the value returns 1. In this way it is possible to read input from buttons.
Remember to deactivate the port:
# echo 408 > unexport

=== Second experiment: write a gpio output (e.g. turn on/off a led diode) ===

Now let us use the same gpio for output.
We can activate the port as before:
# echo 408 > export
'''remove the jumper of the previous experiment!''' and define the port as output:
# echo out > gpio408/direction

Connect a led diode in series with a suitable resistor between pin 13 of U14 and +3.3V (pin 5 of U13). The led anode must be towards +3.3v.
<pre>
(pin 13 of U14) ---/\/\/\/\-----|>|----- (pin 5 of U13)
</pre>

If everything is okay the led should be on.

Now write 1 to the value:
# echo 1 > gpio408/value

And the led will turn off. Obviously, to turn the led back on:
# echo 0 > gpio408/value

The values are reversed because the expander ports are like open collector connections.

At the end remember to deactivate the port:

# echo in > gpio408/direction
# echo 408 > unexport

@@ Riga 60: / Riga 60: @@
 (*) In my tests I use 1Kohm resistors. The led is not very bright at 3.3V but it is safe to use the same "tool" at 5V too.
 <pre>
-(pin 13 of U14) ---/\/\/\/\-----|>|----- (pin 5 of U13)
+(pin 13 of U14) ---/\/\/\/\-----|<|----- (pin 5 of U13)
 </pre>

@@ Riga 57: / Riga 57: @@
    # echo out > gpio408/direction
-Connect a led diode in series with a suitable resistor between pin 13 of U14 and +3.3V (pin 5 of U13). The led anode must be towards +3.3v.
+Connect a led diode in series with a suitable resistor(*) between pin 13 of U14 and +3.3V (pin 5 of U13). The led anode must be towards +3.3v.
 <pre>
 (pin 13 of U14) ---/\/\/\/\-----|>|----- (pin 5 of U13)

@@ Riga 39: / Riga 39: @@
    # cat gpio408/value
 Now, use a 10Kohm resistor to connect the pin 13 of U14 to ground (for example pin 1 of U14) (it works using a jumper, too. The resistor is for safety. It is more unlikely to damage the Chip toy.)
    # cat gpio408/value
@@ Riga 60: / Riga 63: @@
 If everything is okay the led should be on.
 Now write 1 to the value: