ppiotr69
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How many I2C buses does RPI have? (solved)

Thu Oct 09, 2014 7:28 pm

Hello,

How many I2C ports/buses does RPI have?

I can find two devices in the /dev folder: /dev/i2c-0 and /dev/i2c-1
Connecting real 4 hardware devices to
2 devices go to:
I2C1_SDA -> P1-03 / GPIO 2
I2C1_SCL -> P1-05 / GPIO 3
and the second two devices to:
I2C0_SDA -> P5-03 / GPIO28
I2C0_SCL -> P5-04 / GPIO29

i2cdetect -y 1 detects two real devices at 0x3c 0x3d
i2cdetect -y 0 does NOT detect any device.

Wiring is 100% ok.

Does it mean that we have only one I2C bus?

... regards any thanks for your assistance.


EDIT: Solution is described http://www.raspberrypi.org/forums/viewt ... 97#p625297
Last edited by ppiotr69 on Sat Oct 11, 2014 9:16 pm, edited 3 times in total.

ShiftPlusOne
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Re: How many I2C buses does RPI have?

Thu Oct 09, 2014 7:35 pm

The pi has two i2c peripherals. One for the ARM and one for the GPU (used for the camera, for example). It's possible to use the GPU's I2C peripheral, but there's no guarantee that things won't catch fire. For example, the camera on a b+ doesn't work if the i2c module is loaded and i2c0 is enabled.

http://www.raspberrypi.org/forums/viewt ... 28&t=87715

ppiotr69
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Re: How many I2C buses does RPI have?

Thu Oct 09, 2014 8:36 pm

Hello ShiftPlusOne,

Thank you for your prompt answer! I'm going to have just 4 oled displays, so I do not expect any conflicts, however the two cheap ebay/China (non-Adafruit) devices have the same 0x3d & 0x3c addresses. Therefore I decided to "revive" the second bus.
Unfortunately adding bcm2708.vc_i2c_override=1 to cmdline.txt did not help - see the result below. I still cannot detect the devices on /dev/i2c-0 - any idea?

Code: Select all

[email protected]:~# cat /boot/cmdline.txt
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait bcm2708.vc_i2c_override=1
[email protected]:~# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c 3d -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
[email protected]:~# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
[email protected]:~# ll /dev/i2c*
crw-rw-rwT 1 root i2c 89, 0 Oct  9 22:11 /dev/i2c-0
crw-rw-rwT 1 root i2c 89, 1 Oct  9 22:11 /dev/i2c-1
[email protected]:~# uname -a
Linux raspberrypi 3.6.11+ #538 PREEMPT Fri Aug 30 20:42:08 BST 2013 armv6l GNU/Linux
[email protected]:~# cat /etc/udev/rules.d/90-i2c.rules 
KERNEL=="i2c-[0-7]",MODE="0666"
Image
http://i.imgur.com/wOOXpFA.jpg

Massi
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 8:58 am

[ot]
very nice display!
what's that? :)
[/ot]

ppiotr69
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 10:10 am

very nice display! what's that?
This is a China clone of Adafruit I2C Oled display with SSD1306 driver.
http://www.adafruit.com/product/326.
You can have one from ebay or any other provider for less than 6€ just search for "0.96" 128x64 oled"
Some of them have the first 16 lines in yellow, some of them are fully "monochrome" in white or blue colour.
Just two examples you can find on ebay:
Image
Image

Be careful they do differ from this from Adafruit! For example they do not have reset pin and can work only with I2C bus. You won't find (at least I did not) any 100% ready to use library. I'm finishing a bigger project with them and I have adapted some libraries available on Internet. Now I can operate two, but I was hoping to have 4 in parallel.

Or maybe someone has already hacked this display to add another i2c address?

Massi
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 10:36 am

i admit i'm hating you a little now, because i have to get one of those :)

even DX sells some of them, i liked your "two colors" display, but even monocrome is nice..

Quite happy if there is not "ready" code, so i can play with it :) but the first doubt is how you send data to it? i expect you to send binary value for each matrix point? how?

this is going to be funny :)

PS: on dx devices it seems that on the back there's a smd resistor (soldered) that can be moved (i think unsoldering it..) to change i2c address, isn't it the case also of yours?

ppiotr69
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 11:26 am

pattagghiu wrote:i admit i'm hating you a little now, because i have to get one of those :)
Quite happy if there is not "ready" code, so i can play with it :) but the first doubt is how you send data to it? i expect you to send binary value for each matrix point? how?
PS: on dx devices it seems that on the back there's a smd resistor (soldered) that can be moved (i think unsoldering it..) to change i2c address, isn't it the case also of yours?
I send the complete 128x64 matrix every time I want to update the screen. Therefore It is necessary to perform all operation in memory table and update the real screen only if necessary after we have completed one full screen modification cycle. Enclosed part of the "update" routine.

Code: Select all

bool OLED::WriteScreen (void)
{
    bool fOK;
    WORD uiIndex = 0x00;
    BYTE uchTemp[0x09];

    fOK = i2cWriteCmd (0x21, 0x00, 0x7F); 
    fOK = i2cWriteCmd (0x22, 0x00, 0x07); 

    while (uiIndex < (WIDTH * HEIGHT))
    {
        uchTemp[0] = 0x40;      
        for (int i = 0; i < 8; i++)  
            uchTemp[i+1] = uchpBuffer[uiIndex+i];
        fOK = i2cWrite (uchTemp, 0x09); 
        uiIndex += 0x08;
    }

    return fOK;
}
It is probably possible to address every single pixel
i2cWriteCmd (0x21, start, end); // Set column address; start and end
i2cWriteCmd (0x22, start, end); // Set row address; start and end
but I did not really care about this, since I corrected existing library for 128x32 to work with 128x64 displays.

Here you can find some more interesting information:
http://hallard.me/adafruit-ssd1306-oled ... pberry-pi/
I do not use this library, because it is too complex for my purpose. But as far as I can remember it is fully working one.

Addressing:
This is even not a smd resistor! It is smd jumper with 0 ohm resistance. And of course I used it (changed soldering) to have at least two devices on one bus. I can operate two screens in parallel.

As soon as I will be ready with some code sanity I can post my results here to share the libraries and ideas.

Massi
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 12:17 pm

ok ok, i'll take one of them and i'll loose my nights trying to have python scripts to manage them
:)

ps: finally i understood why you said that you use two of them on single bus :)

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0xFF
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 5:09 pm

There is another i2c bus accessible via HDMI:

http://blog.koalo.de/2013/11/i2c-over-hdmi.html

ppiotr69
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 5:27 pm

There is another i2c bus accessible via HDMI: http://blog.koalo.de/2013/11/i2c-over-hdmi.html
not bad! didn't know that.

But also this blog has been mentioned that:
> two interfaces are accessible via P1 and P5
... and I cannot access this on P5 which must be available via: /dev/i2c-0
as already mentioned I've added bcm2708.vc_i2c_override=1 to /boot/cmdline.txt but it does not help.
I cannot detect any device on this interface /dev/i2c-0 (P5).

Has someone already run both /dev/i2c-0 and /dev/i2c-1 buses?

ShiftPlusOne
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 5:28 pm

Of course, they work just fine.

ppiotr69
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 9:01 pm

ShiftPlusOne wrote:Of course, they work just fine.
Great, do you have any idea why I cannot get the the devices detected on the "0" bus?

... and adding bcm2708.vc_i2c_override=1 to /boot/cmdline.txt cannot help because I'm still on kernel 3.6.11+
and I do not want to change it due to some other module dependencies (easycap / stk1610) I prefer to keep.

So in my kernel there is no board and "vc_i2c_override" identification:
file: bcm2708.c and in function: void __init bcm2708_init(void) there is unconditional
bcm_register_device(&bcm2708_bsc0_device);
bcm_register_device(&bcm2708_bsc1_device);
therefore i'm getting these two devices /dev/i2c-0 and /dev/i2c-1 independent from the parameter.
There must be another problem, which I'M not aware of and I would appreciate your hep.
Last edited by ppiotr69 on Fri Oct 10, 2014 9:43 pm, edited 1 time in total.

ShiftPlusOne
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 9:03 pm

Nope, I'd need the setup here to probe around and see what's going wrong, if anything.

ppiotr69
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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 9:50 pm

Hi ShiftPlusOne,
>Nope, I'd need the setup here to probe around and see what's going wrong, if anything.
thank you anyway fro your support, you can look to my previous post, I updated with some other findings.
If you have any spontaneous idea please let me know. However I've given up and I stay with two displays for the moment.
Many regards
P.

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Re: How many I2C buses does RPI have?

Fri Oct 10, 2014 10:02 pm

My original post was addressing the title of your thread (how many I2C buses there are). I did notice that in the body of the text you mentioned that i2c-0 shows up, indicating that you're running an old kernel, but figured it was worth addressing the title of the thread anyway.

Can you get your hands on an oscilloscope? That will be an easy way to tell if you are getting data out of i2c0 and whether the devices are sending an ACK.

ppiotr69
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 12:33 am

ok, then i will keep you busy :)
I've got scope - but a very old one with one analog channel.
What I have done I run in a bash loop:

Code: Select all

while true; do i2cdetect -y 1; done
and observe SDA - a nice square signal
the same for:

Code: Select all

while true; do i2cdetect -y 0; done
results in no signal change - the SDA line (P5-03 / GPIO28) is constantly high
Then I tried if the pins are still alive:

Code: Select all

gpio mode 17 out; while true; do gpio write 17 0; gpio write 17 1; done
produces again a "nice" square signal

so we are again at the beginning :(

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joan
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 5:19 am

You'll at least need to set the I2C SDA/SCL gpios to mode ALT0. Otherwise they are just ordinary gpios. Check the current mode.

ppiotr69
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 11:27 am

Hi joan,

good point, however after changing the mode for these two pins the status is the same - no devices on i2c-0 - see screen snapshot below:

Code: Select all

[email protected]:~# gpio mode 17 ALT0 && gpio mode 18 ALT0 ; gpio readall ; gpio load I2C 100 ; i2cdetect -y 0 ; i2cdetect -y 1
 +-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
 |   2 |   8 |   SDA.1 | ALT0 | 1 |  3 || 4  |   |      | 5V      |     |     |
 |   3 |   9 |   SCL.1 | ALT0 | 1 |  5 || 6  |   |      | 0v      |     |     |
 |   4 |   7 | GPIO. 7 |   IN | 0 |  7 || 8  | 1 | ALT0 | TxD     | 15  | 14  |
 |     |     |      0v |      |   |  9 || 10 | 1 | ALT0 | RxD     | 16  | 15  |
 |  17 |   0 | GPIO. 0 |  OUT | 0 | 11 || 12 | 0 | IN   | GPIO. 1 | 1   | 18  |
 |  27 |   2 | GPIO. 2 |  OUT | 0 | 13 || 14 |   |      | 0v      |     |     |
 |  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
 |     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
 |  10 |  12 |    MOSI | ALT0 | 0 | 19 || 20 |   |      | 0v      |     |     |
 |   9 |  13 |    MISO | ALT0 | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
 |  11 |  14 |    SCLK | ALT0 | 0 | 23 || 24 | 1 | ALT0 | CE0     | 10  | 8   |
 |     |     |      0v |      |   | 25 || 26 | 1 | ALT0 | CE1     | 11  | 7   |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |  28 |  17 | GPIO.17 | ALT0 | 1 | 51 || 52 | 1 | ALT0 | GPIO.18 | 18  | 29  |
 |  30 |  19 | GPIO.19 |   IN | 0 | 53 || 54 | 0 | IN   | GPIO.20 | 20  | 31  |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c 3d -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
[email protected]:~# 
Please assume that I do not know what I'm doing - what I can do next?
--------
Edit (5 minutes later)
There is a difference - now when I run "while true; do i2cdetect -y 0; done" I'm getting square signal on SDA pins.
I will check wiring again and update the post.
Last edited by ppiotr69 on Sat Oct 11, 2014 11:41 am, edited 1 time in total.

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joan
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 11:32 am

Could you confirm this is a late model B with gpios 28-31 brought out to P5? If so I'll have a look at mine to see what has changed.

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joan
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 11:35 am

Also I think you have to switch off ALT0 on gpios 0/1 otherwise that is used preferentially for I2C.

ppiotr69
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 12:03 pm

joan wrote: 1. Could you confirm this is a late model B with gpios 28-31 brought out to P5? If so I'll have a look at mine to see what has changed.
2. Also I think you have to switch off ALT0 on gpios 0/1 otherwise that is used preferentially for I2C.
1-> Yes this is the "late" B model with output P5 header.
2-> To what mode I have to switch gpios 2/3? I need two working i2c buses i2c-0 and i2c-1

I think that now i2c-0 somehow is alive
the sequence: "while true; do i2cdetect -y 0; done" produces a square signals on P5 I2C clock and data lines.
Unfortunately I do not have any digital scope to analyse what is going on on the data line in order to check if the display responses with ACK to the incoming requests from "i2cdetect -y 0".

Hardware is ok, I can switch the displays between i2c-1 and i2c-0 and they work just fine.
However a new question / doubt:
I have 4 displays two of them have the 0x3D address and the second two have 0x3C.
Are the buses i2c-0 and i2-1 seen from the RPI as a independent ones? Can I operate devices with the same addresses on these two buses? Could it be that this is the issue?

My RPI:
Image
http://i.imgur.com/pCMM4TB.jpg

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joan
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 12:08 pm

The buses are independent.

piscope may be useful as long as you limit the bus speed to 100kbps. pigpio samples at 200kbps by default so if the bus is run at 400kbps the data will be misleading.

ppiotr69
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 2:16 pm

@joan
it looks like that it's your tool and it works great.
But I'm too weak to find out "manually" what is going on on the data bus. Would you like to check the results? I attached the dump data. I run one detect on i2c-1 and one on i2c-0 they look quite similar. i2c-0 repeated probably the bus scan.
Attachments
i2c-dump.piscope.zip
(1.94 KiB) Downloaded 76 times

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joan
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Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 3:14 pm

You seem to have activity on both buses.
ppiotr69-i2c-1.png
ppiotr69-i2c-1.png (43.32 KiB) Viewed 7550 times
The buses appear to be running at 400kbps so piscope is not resolving any detail apart from the start and end of each transaction. You'd need to drop the bus rate to 100kbps to properly see the clock and data lines.

You seem to be getting activity on gpios 0/1 at the same time as gpios 28/29 which I did not expect. I thought the I2C hardware would only drive one pair of gpios. I'd switch gpios 0/1 to mode input as they may be causing a problem.

To change the I2C bus speed you could

sudo rmmod i2c_bcm2708
sudo modprobe i2c_bcm2708 baudrate=100000

It's best to run the daemon at a higher sample rate as well

close piscope
sudo killall pigpiod
sudo pigpiod -s 2 -x -1 # -1 gives write access to all gpios

pigs m 0 r # switch gpio 0 to input
pigs m 1 r

ppiotr69
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[SOLVED] Re: How many I2C buses does RPI have?

Sat Oct 11, 2014 5:26 pm

Dear joan,

You solved my problem! The solution has been mentioned already in your earlier posts. I would appreciate if you however can explain me following thing:
with this two commands:
pigs m 0 r
pigs m 1 r
you switch the GPIO.0 and GPIO.1 (naming of rev 1) or GPIO.2 and GPIO.3 (naming in rev 2) hardware: P1-03 and P1-05 into Input/read mode. Right? How can I do this with simple gpio command? Can I?
Numbers 0 and 1 indicate somehow the old rev 1 pins or what?

Current solution summary (all commands as root)
To enable the two I2C buses it is necessary to:
1) add parameter: bcm2708.vc_i2c_override=1 to /boot/cmdline.txt (for all new kernels)
2) change mode of P5-03/GPIO28 and P5-04/GPIO29 to ALT0 with command: gpio mode 17 ALT0 && gpio mode 18 ALT0
3) (now comes the magic) switch off ALT0 on gpios 0/1 otherwise that is used preferentially for I2C.
3.1) run: pigpiod -s 2 -x -1
3.2) run: pigs m 0 r
3.3) run: pigs m 1 r
and that's it - we have two i2c buses:

Code: Select all

[email protected]:~# i2cdetect -y 0 ; i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c 3d -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c 3d -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --     
Thank you guys for your time and support.
Joan look forward to your explanation how to bypass your pigpiod demon. I do not want to start something i use only once at the beginning. It has nothing to do with dislike of your tool :)

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