Making an LCD adapter board

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1

This is largely wishful thinking on my part but I recently bought a Beagleboard Rev C2, which by today’s standards is ancient. I know nothing about PCB design but I saw these LCD headers space on the board and info in the docs about an adapter board. I bought a 7" Innolux digital TFT LCD (and a touch screen, which is another matter) and am trying to figure out how the 40 pin connector on the LCD relates to the 2 x 20 pin space on the Beagle. Below are the tables for the two banks of Beagle headers and that for the 40 pin assignment of the LCD.

I notice there are 26 Os (outputs) on the Beagle and an equal number of Is (inputs) on the LCD. Do they correlate? How does one go about making the connections/correlations? Is this one of those projects that can be accomplished using a PCB from my neighbourhood electronic shop and a printer? I’ve also copied and pasted some power data on the LCD below. I’d really appreciate your patience, guidance and help, thanks.

8.14 LCD Expansion Headers (Rev C2 only)

Access is provided on the Rev C2 to allow access to the LCD signals. Table 16 shows the signals that are on the J4 connector. You will notice that the signals are not in a

logical order or grouping. This is due to the routing on the PCB where we allowed the routing to take president to get it to rout with no addition of layers to the design.

Table 16. J4 LCD Signals



Pin#

Signal

I/O

Description


















1

DC_5V

PWR

DC rail from the Main DC supply


2

DC_5V

PWR

DC rail from the Main DC supply


3

DVI_DATA1

O

LCD Pixel Data bit


4

DVI_DATA0

O

LCD Pixel Data bit


5

DVI_DATA3

O

LCD Pixel Data bit


6

DVI_DATA2

O

LCD Pixel Data bit


7

DVI_DATA5

O

LCD Pixel Data bit


8

DVI_DATA4

O

LCD Pixel Data bit


9

DVI_DATA12

O

LCD Pixel Data bit


10

DVI_DATA10

O

LCD Pixel Data bit


11

DVI_DATA23

O

LCD Pixel Data bit


12

DVI_DATA14

O

LCD Pixel Data bit


13

DVI_DATA19

O

LCD Pixel Data bit


14

DVI_DATA22

O

LCD Pixel Data bit


15

I2C3_SDA

I/O

I2C3 Data Line


16

DVI_DATA11

O

LCD Pixel Data bit


17

DVI_VSYNC

O

LCD Vertical Sync Signal


18

DVI_PUP

O

Control signal for the DVI controller. When Hi, DVI is enabled. Can be used to activate circuitry on adapter board if desired.


19

GND

PWR

Ground bus


20

GND

PWR

Ground bus

The current available on the DC_5V rail is limited to the available current that remains from the DC supply that is connected to the DC power jack on the board. Keep in mind that some of that power is needed by the USB Host power rail and if more power is needed for the expansion board, the main DC power supply current capability may need to be increased. All signals are 1.8V except the DVI_PUP which is a 3.3V signal.

Table 17 shows the signals that are on connector J5.

Table 17. J5 LCD Signals



Pin#

Signal

I/O

Description


1

3.3V PWR

3.3V

reference rail


2

VIO_1V8

PWR

1.8V buffer reference rail.


3

DVI_DATA20

O

LCD Pixel Data bit


4

DVI_DATA21

O

LCD Pixel Data bit


5

DVI_DATA17

O

LCD Pixel Data bit


6

DVI_DATA18

O

LCD Pixel Data bit


7

DVI_DATA15

O

LCD Pixel Data bit


8

DVI_DATA16

O

LCD Pixel Data bit


9

DVI_DATA7

O

LCD Pixel Data bit


10

DVI_DATA13

O

LCD Pixel Data bit


11

DVI_DATA8

O

LCD Pixel Data bit


12

NC





No connect


13

DVI_DATA9





LCD Pixel Data bit


14

I2C3_SCL

I/O

I2C3 Clock Line


15

DVI_DATA6

O

LCD Pixel Data bit


16

DVI_CLK+

O

DVI Clock


17

DVI_DEN

O

Data Enable


18

DVI_HSYNC

O

Horizontal Sync


19

GND

PWR

Ground bus


20

GND

PWR

Ground bus

The 1.8V rail is for level translation only and should not be used to power circuitry on the board. The 3.3V rail also has limited capacity on the power as well. If the TFP410 is disabled on the Beagle, then 80mA is freed up for use on an adapter card connected to the LCD signals connectors. It is not required that the TFP410 be disabled when running an adapter card, but the power should be taken into consideration when making this decision.

It is suggested that the 5V rail be used to generate the required voltages for an adapter card.

Innolux AT070TN83 V.1 Pin Assignment

TFT LCD Panel Driving Section

TTL Connector is used for the module electronics interface. The recommended model is

FH19SC-40S-0.5SH manufactured by Hirose.



Pin No.

Symbol

I/O

Function

Remark


1

VLED

P

Power voltage for LED Driver





2

VLED

P

Power voltage for LED Driver





3

ADJ

I

Adjust the led brightness with PWM Pulse

Note 1;2


4

GLED

P

Ground for LED circuit





5

GLED

P

Ground for LED circuit





6

VCC

P

Power voltage for digital circuit





7

VCC

P

Power voltage for digital circuit





8

MODE

I

DE or HV mode control

Note 3


9

DE

I

Data enable





10

VS

I

Vsync signal input





11

HS

I

Hsync signal input





12

GND

P

Power ground





13

B5

I

Blue data input (MSB)





14

B4

I

Blue data input





15

B3

I

Blue data input





16

GND

P

Power ground





17

B2

I

Blue data input





18

B1

I

Blue data input





19

B0

I

Blue data input(LSB)





20

GND

P

Power ground





21

G5

I

Green data input(MSB)





22

G4

I

Green data input





23

G3

I

Green data input





24

GND

P

Power ground





25

G2

I

Green data input





26

G1

I

Green data input





27

G0

I

Green data input(LSB)





28

GND

P

Power ground





29

R5

I

Red data input(MSB)





30

R4

I

Red data input





31

R3

I

Red data input





32

GND

P

Power ground





33

R2

I

Red data input





34

R1

I

Red data input





35

R0

I

Red data input(LSB)





36

GND

P

Power ground





37

DCLK

I

Sample clock





38

GND

P

Power ground





39

L/R

I

Select left or right scanning direction

Note 4


40

U/D

I

Select up or down scanning direction

Note 4

I: input; O: output; P: power

Note1: ADJ adjust brightness to control Pin, Pulse duty the bigger the brighter.

Note 2: ADJ signal=0~3.3V,operation frequency:100~300Hz.

Note 3: DE Mode, Mode=”H”,HS floating and VS floating

HV Mode, Mode=”L” and DE floating

Note 4: Selection of scanning mode

3.2. Typical Operation Conditions

Item

Symbol

Values

Unit

Remark

Min.

Typ.

Max.

Power voltage

VCC

3.1

3.3

3.5

V

Note 1

VLED

4.8

5.0

5.2

V

Note 2

Current consumption

Icc

2

Your email was clipped because of its size. No need to reprint the manual. I have read it before. You would be better off attaching the datsheet for your LCD. I should be able to explain to you the comcept of RGB signals and if your LCD supports that, and give you a mapping between the two.

I will say this, you will most likely need to make an adapter board for this to work. Beagle has 1.8V I/O and most LCDs out there are at least 3.3V. So, you will need to design a PCB to get this to work with your LCD panel.

Gerald

3

OK gerald, here’s the data sheet in PDF. I had just copied portions.

AT070TN83.pdf (930 KB)

4

This looks compatible. Take a look at the BeagleBoard-xM schematic page 9, and you will find a mapping of the LCD signals for Red Green and Blue to line up with the signals names used on the schematic. You can then map them to the LCD headers and to your LCD. This LCD is 3.3V, so you will need to create a voltage level translation board that will change the levels form 1.8V to 3.3V.

Gerald.

5

Thanks Gerald. Now to google “voltage level translation” and see what that yields.

Mark.

6

You will need a buffer that converts 1.8V to 3.3V and it needs to run at fairly high speed to handle the frequency of the signals. Something like a SN74AVC32T245.

Gerald

7

Do I buy one of these as a starter?:

8

Well, they are surface mount parts. You will need to make a PCB, solder them to the PCB, and then wire the LCD signals to it.

Gerald

9

Hi Gerald,

I looked at the LCD RGB interface in the schematic and that seems mapped to the DVI_DATA. Since there are only 18 RGB signals on my LCD I’m guessing it’s 18 bit and not 24 as the Beagle. A note on the drawing says to refer to Section 15.2 of the Processor Technical Reference Manual for modes other than 24 bit.

I checked the OMAP35x Applications Processor Technical Reference Manual where section 15.2.2.5.2 details 18 Bits per Pixel (Loosely Packed) - RGB Color Format, Long Packet; and section 15.2.2.5.3 addresses 18 Bits per Pixel (Packed) - RGB Color Format, Long Packet. What I don’t see is something that maps the signal symbol to the function as on the schematic. Another point of your finger would be of great help (before I launch Kicad and find ‘PCB for Dummies’). Thanks.

Mark.

10

Set it up as 6 6 6 data and tie the 2 LSB on th eLCD to GND…

Gerald

11

Thanks. Making much progress. Just dropped a 2x10 connector on a blank schema. Tomorrow when I get to setting up “6 6 6 data” I’ll ask the next question. But preliminary questions. (1) On the LCD there are R, G and B LSB (three) and MSB (three). What to do with the extra LSB and the three MSBs? (2) Should I just follow the numbering order of the other six? I really am just a media strategist writer/editor so bear with me.

If this work’s I’ll add it to the public repository with the step by step.

Mark.

12

Connect the top six MSB signals of each group to your LCD and leave the rest unconnected.

Gerald

13

Hi Gerald,
I got the SN74AVC32T245ZKER transceivers and a 40 pin connector for the cable from DigiKey. I’m trying to use Eagle and other free/open source PCB/schematic designers but none seems to have a SN74AVC32T245ZKER component. Eagle has some 16 bit TI transceivers but not this. (1) Is there some library where this component can be found?

(2) The LCD VLED requires 5V and the Rev C2 manual says “It is suggested that the 5V rail be used to generate the required voltages for an adapter card.” Should I connect the adapter card to pin 1 or 2 on J4?

(3) Re J5, the manual says “The 1.8V rail is for level translation only and should not be used to power circuitry on the board. The 3.3V rail also has limited capacity on the power as well.” Do I need to pass the 3.3V (pin 1 J5) through the transceiver; and should all the signals from the LCD header be passed through the transceiver as well and converted to 3.3V?

(4) How do I configure the transceiver to convert from 1.8V? The literature I’ve found says it’s configurable but I don’t grasp how.

Thanks.

Mark.

14

Below.
Gerald

Hi Gerald,
I got the SN74AVC32T245ZKER transceivers and a 40 pin connector for the cable from DigiKey. I’m trying to use Eagle and other free/open source PCB/schematic designers but none seems to have a SN74AVC32T245ZKER component. Eagle has some 16 bit TI transceivers but not this. (1) Is there some library where this component can be found?

I gues you need to make your own symbol for Eagle

(2) The LCD VLED requires 5V and the Rev C2 manual says “It is suggested that the 5V rail be used to generate the required voltages for an adapter card.” Should I connect the adapter card to pin 1 or 2 on J4?

Where is J4?

(3) Re J5, the manual says “The 1.8V rail is for level translation only and should not be used to power circuitry on the board. The 3.3V rail also has limited capacity on the power as well.” Do I need to pass the 3.3V (pin 1 J5) through the transceiver; and should all the signals from the LCD header be passed through the transceiver as well and converted to 3.3V?

You need to convert the 5V to 3.3V and use it for your 3.3V rail. Connect the 1.8V to the Beagle side of your level shifter and the 3.3V from the regulator to the other side.

(4) How do I configure the transceiver to convert from 1.8V? The literature I’ve found says it’s configurable but I don’t grasp how.

All you have to do is connect the voltages for A and voltages for B, set the enable pins, and set the direction pins. That is in the datasheet in a table on how to do that.

I suggest we take this off the list and communate direct so that we do not oveflow everyone’s mail boxes…

15

Hi Gerald,
I got the SN74AVC32T245ZKER transceivers and a 40 pin connector for the
cable from DigiKey. I'm trying to use Eagle and other free/open source
PCB/schematic designers but none seems to have a SN74AVC32T245ZKER

<rant>
As an aside, it really is about time that manufacturers and retailers
started publishing Eagle (or some other well defined format that can
be transformed easily) descriptions for their products as a matter of
course, and that retailers should link to these files with the product
description on their web sites. Perhaps if we all started asking for these
files they would wake up. Our only sanction would be not to buy products
which do not have these files available.
</rant>

David

16

If you are making a PCB you should also consider adding supply circuit
for LCD backlight. If you are considering adding touchscreen too, then
touchscreen controller should also placed there... By the way, a good
example is the schematic of the TI EVM board...

17

Thanks Pityuka. I think the backlight is the 5V. Do you mean should place the touchscreen on a circuit with the backlight?

Do you have a link to the schematics?

Mark.

18

The link from TI website (http://focus.ti.com/docs/toolsw/folders/
print/tmdsevm3530.html) takes you to Mistral (http://
www.mistralsolutions.com/pes-support/support-downloads/omap3-evm-documentation-a-software-.html#
), from where the files can be downloaded. Registration is required
but it is free.

If the backlight requires only 5V, then you may not need additional
circuits, except for switching it on/off if needed. What I meant is if
you're designing an expansion board for the LCD, besides the level
converters there may be circuits related to the LCD like backlight,
touch screen control that I would surely place on the same expansion
board....

Pityu

19

You will need to register to download it.

http://www.mistralsolutions.com/pes-support/support-downloads/omap3-evm-documentation-a-software-/tmdxevm3530.html

Gerald

20

Hey guys, I would like to say that I find this thread very interesting
and look forward to any progress made on schematics or a final
product... my beagle is in storage at the moment, but I look forward
to trying this when I get it back and some more free time.

-Jim