Resistive touchscreen with 5-wire connection & Freescale IMX28

Question

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?

Answer 1

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.

Answer 2

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
LRADC2 UL
LRADC3 LL
LRADC4 UR
LRADC5 LR
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)