I have a IMX28EVK board and I would like to to connect this board to a 5-wire resistive touchscreen. In the Reference Manual of the I.MX28, Freescale said:

LRADC2 - 6 can be used for 4/5-wire touch-screen control. LRADC6 can be used for the wiper of 5-wire touch-screen controller and external temperature sensing, but they cannot be enabled at the same time in hardware configuration. LRADC5 can be used for Y- of 4-wire and LR of 5-wire; LRADC4 can be used for X- of 4-wire and UR of 5-wire; LRADC3 can be used for Y+ of 4-wire and LL of 5-wire; LRADC2 can be used for X+ and UR of 5-wire; For pull-up or pull-down switch control on LRADC2~5 pins, please refer to HW_LRADC_CTRL0 register.

I think that there's an error. The word UR is repeated 2 times and UL never appears

I have this touchscreen:

Model: EL-TS-104F-5H Type: Analog resistive 5 wire B-type.

This touchscreen has 5 pin:

1 - RT; 2 - RL; 3 - SG; 4 - LT; 5 - LL

|LT      RT|
|          |
|LL      RL|

I've made this connection:

RT <-> UR
RL <-> LR
SG <-> wiper
LT <-> UL (?)
LL <-> LL

But the touchscreen doesn't work properly. Is the connection that I've made is correct? If not, what's the right connection? Any suggestions?

  • 1
    \$\begingroup\$ I've got the same EVK and a custom board based on the MX283. (No LCD or touchscreen, however) What steps did you take in LTIB or kernel configuration? You may need to look at the linux/arch/arm/mach-mx28/ platform files and modify the LRADC configuration that way. I'm assuming you have a working LCD? Most likely, the Freescale MX forum would be better for this question. \$\endgroup\$
    – darron
    Jun 9, 2011 at 18:28
  • \$\begingroup\$ I have the evk and my custom board. I also have the evkLCD with touch (4-wire) and another LCD with touch (5-wire).<br> No problem with LCD, all working properly, also the 4-wire touch.<br> I think that LTIB is configured right, but is possible that I was wrong.<br> Do you think that is possible that the LTIB is configured for only 4-wire touch and not for 5-wire? However i will go check the platform file. <br> Thanks for the hint.<br> \$\endgroup\$
    – Katte
    Jun 10, 2011 at 6:42
  • \$\begingroup\$ Ok, probably I need to reconfigure LTIB. Maybe I need to use a different driver or to create a new one.. Thanks for the hint. \$\endgroup\$
    – Katte
    Jun 10, 2011 at 7:09
  • 4
    \$\begingroup\$ is this reference manual online? And if so could you provide a link? Thanks! \$\endgroup\$
    – dhsieh2
    Jun 19, 2011 at 16:32

2 Answers 2


I'm just spit ballin here but why would you connect RL to LR if you've connected RT to UR? Swap UL and LR connections and see what happens. It just seems like you would connect the L's to the L's and then obviously SG goes to wiper, so that leaves the U's to go to the R's so put RL and UL together.

I can't find any documentation related to the touchscreen mentioned so this is the best I got.

  • \$\begingroup\$ No, The connections should by symbolically correct. I read them as "RT" = RightTop, UR = UpperRight. I'm guessing they got UR wrong on the MX28 side... since they seem confused about it. It turns out LRADC2 is for UL, based on a figure on another page in the reference manual. \$\endgroup\$
    – darron
    Jan 3, 2014 at 5:06
  • \$\begingroup\$ Ah, okay that is pretty logical. Honestly without any documentation, I can't help you. \$\endgroup\$
    – Funkyguy
    Jan 3, 2014 at 5:11
  • 1
    \$\begingroup\$ Not me, Katte... back in June 2011. I guess Kortuk just wants this ghost question answered. :) \$\endgroup\$
    – darron
    Jan 3, 2014 at 5:18
  • \$\begingroup\$ @darron 17 votes up and no answer, it needed some love. \$\endgroup\$
    – Kortuk
    Jan 6, 2014 at 17:59

To answer the initial confusion on the typo concerning which LRADC pin is which... the iMX28 Reference Manual shows a Figure 38-2 on page 2269 with the following pin definitions:

LRADC0 button 0
LRADC1 button 1
LRADC6 wiper

You'd also need to configure the HW_LRADC_CTRL0 register to disable any pullups or pulldowns on those lines. (Although selecting the appropriate touchscreen driver would probably do that for you)

The connections to the mentioned 5-wire device should be correct... as RT should mean "Right side top" and be equivalent to UR ("upper right").

The configuration of LTIB selecting the touchscreen driver and enabling all this may be an issue, but I'd guess this should work out of the box for the demo board and it's standard image. (Unless it's set up for 4-wire or something)


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