Tour : click picture below for previous

Back to Mike's Electric Stuff

Click picture below for next



Ipod Video LCD hacking

More LCD hacking here

 

Looking for a small, cheap LCD for a possibly large-scale project, I decided that the 2.5" QVGA TFT in the Ipod Video may be worth a look, as cheap clones of it are available from Hong Kong via Ebay..
Not finding any info on this unit on the net, I decided to investigate myself, & bought a faulty ipod on Ebay to dissect. The hard disk was dead, but I could get it into service test mode, which was all I needed to fiddle with the display to see how it was driven.

First problem was that the connector is a 0.3mm pitch FFC, so somewhat fiddly to connect to......  but I'm not easily defeated by fiddliness, and have a really good magnifier..
The FFC connector is staggered, with pins on alternate sides, so the wires soldered on to it are 0.6mm apart. I also needed to keep them very tidy & flat to stop them fouling the flex cable entry and locking lever.

wpeE0.jpg (57950 bytes)wpeF1.jpg (17974 bytes)

wpeE1.jpg (502325 bytes)

I'd been reading a few controller datasheets, so had a good idea of what I was looking for. After identifying the power and ground pins, some probing with the scope pretty soon found what looked like the control lines - WR,RD,CS,RS. This left exactly 16 more signals - the data bus.

A major stroke of luck was that the test mode had some screen tests which displayed a graduated scale from black to each primary colour, so the RGB values counted upwards through the frame. This made identifying which pins mapped to R,G,B pretty trivial :  

wpeEF.jpg (40453 bytes)wpeF6.jpg (119751 bytes)


I assumed that the bus was mapped from D0..15 along the pins, and this appears to be confirmed by looking at the commands sent at the start of a frame, which contained values corresponding to the 320x240 resolution ( see later)

Took a while to find the connector manufacturer - it's a 32 way 0.3mm pitch ZIF FFC - and unusually has an even number of pins and reverse-side latch. Couldn't find it from HRS,JAE, JST or Molex. Then I noticed the connector on the hard disk had a similar style of latch, so looked up the HD on the Toshiba site & found a datasheet listing the connector manufacturer. It's a DDK FF12 series, part number FF12-32A-R11A. I've also seen an Omron part used on another ipod PCB, and it looks like the part number should be XF2B-3245-31A, but the datasheet for this series doesn't list a 32 way option.

I enquired with a DDK distributor about availablility, and found that the minimum order is not just one reel, which I sort of expected, but three (7500 connectors), at GBP0.71 each.
I think I'll have to see if it's feasible to use a more readily available 33 pin connector.....

wpeF7.jpg (21066 bytes)

Connector pinout (I've called pin 1 as shown above - nearest the edge of the LCD frame)
Pin Function
1 Not Used
2 3.1V Supply
3 1.8V Presumably I/O supply. All I/Os run at 1.8v levels.
hopefully this pin can be set to 3V or 3.3v for 3V IO - I'll wait til I have ID'd the controller, or have an expendable display before testing this!
4 0V
5 /Reset.
6 /CS  Chip select
7 /WR  write strobe
8 RS Selects command/data register ( called CD in some datasheets)
9 /RD read strobe
Data bus Colour
10 D0 Blue 0
11 D1 Blue 1
12 D2 Blue 2
13 D3 Blue 3
14 D4 Blue 4
15 D5 Green 0
16 D6 Green 1
17 D7 Green 2
18 0V
19 D8 Green 3
20 D9 Green 4
21 D10 Green 5
22 D11 Red 0
23 D12 Red 1
24 D13 Red 2
25 D14 Red 3
26 D15 Red 4
27 0V
28 Vsync out. Goes high for 84.5us at  frame rate of 47Hz
29 0V
30 Backlight -
31 Backlight + Vf is 13.7V ( 4 white LEDs in series)
32 Not used

 

Next step is to try to identify the controller. One way will be to look at the commands and try to match with possible chips for which I have data. But will post a few requests on the net to see if anyone already knows.... It should be possible to figure out how to drive it without the data, by logging the commands, but there may be some more interesting features that can be used once the controller is identified.

If you know for sure what controller this LCD uses, please let me know!

The register structure looks similar to the Toshiba JBT6K71, but registers are used that do not exist on that part, so best guess so far is it's another one in the Toshiba range.

possibles ( not checked yet) : JBT6K98,

Eliminated so far : JBT6K71, R61503, LDS285,S6D0154,ILI9320,S1D19122,JBT6K74A,JBT6K85,

 


Initialisation sequence 

Start of initialisation - Burst at end of trace is main initialisation sequence shown below. The six pulses inbetween are writes of 0000 with RS low.

wpeF4.jpg (104163 bytes)

Start of main initialisation

bwpeF5.jpg (122100 bytes)

Initialisation sequence
Write 00 with RS low
Read with RS high - returns 3401 - probably device type identifier
(It is possible that the firmware supports multiple controller types based on this ID....)
Commands in the list below consist of :

Write of address with RS low, then write of data with RS high.
Rewrite of same address with RS low, and readback with RS high - presumably to verify written value - I doubt it's necessary. I also suspect the register address is probably incremented after each write.

The first of these (write of 0100 to 0001 is shown in the trace above.

 

Address (hex) Data ( hex) Function
0001 0100
0002 2500
0003 02b0
0004 0000
0008 0404
0009 0000
000b 0000
000d 00b4
0010 0018
0011 2600
0012 2200
0013 0802
0014 080c
0015 0816
0016 2200
0031 0000
0080 0031
0400 001d The sequence up to & including this write is repeated on powerdown
0300 0705
0301 0006
0302 0302
0303 0303
0304 0300
0305 0103
0306 001f
0307 0705
0308 0006
0309 0302
030a 0303
030b 0300
030c 0203
030d 001f
0401 0001
0007 0001
0205 0060
0110 0001
0100 15b0
0101 0020
0102 029d
0103 0e5b
0105 0103
0106 0103
0007 0021
0102 02bd

Sequence on powerdown (Power to LCD is removed on switchoff, so this command may not be to put display in powerdown mode!)

Steps 0001 to 0400 above, then :
0007 0032 ? power control?

Sequence when writing new frame of image data

Command ( write with RS low) Data ( write with RS high) Function
0210 0000 First X co-ordinate of window to write
0211 013f Second X co-ordinate of window to write
0212 0000 First Y co-ordinate of window
0213 00ef Second Y co-ordinate of window
0200 0000 ?( these two commands are listed as 'write RAM address' in JBT6K71A datasheet)
0201 0000 ?
0202 Write-data command ( JBT6K71A data lists as data read/write)
<RGB data>

 

Access timing - command

wpeE0.jpg (97372 bytes)

 

Access timing - Data - rate is 5.5MHz. Full frame write takes 14.2mS

wpeE9.jpg (105034 bytes)

 

 

 


Driving it youself.

This display should be drivable from most microcontrollers ( *I've not yet verfied that it can do 3.3v I/O. If not, you'll need  alot of resistors, or a level shifter), however the 16 bit data bus will need rather alot of  I/O pins. If you're running from something like a NXP LPC2xxx ARM processor, this may not be a big deal, and you may want the speed of the 16 bit bus.

However there are a couple of simple ways to cut down the number of   I/O pins needed, at the cost of extra components, and speed. They also assume you're using the display in write-only mode, and so would not be suitable if, for example, you wanted to read out the display RAM contents.  A write-only interface could leave RD tied high ( assuming the initialisaiton sequence doesn't require the read - seems unlikely). You might also be able to tie CS and WR together.

1) 8 bit latch. Use an 8 bit I/O port to drive the bottom 8 data lines. Connect an 8 bit latch like a 74HC574 with its inputs to the 8 bit port, and the outputs to the top 8 bits  of the display's data bus. Connect the latch clock to another I/O pin. To write a 16 bit value, output the MSbyte to the port, wiggle the clock pin, then output the LSbyte and wiggle the LCD's CS/WR pins.
You should be able to share the latch clock with WR to avoid needing an extra IO pin - the HC574  will latch data on the rising edge, so the LCD module will ignore the latch pulse when CS is high, and the latch data will have been read by the LCD when WR goes high after the write with CS low. 

2) Shift register. Use two 8-bit shift registers, e.g. 74HC164, driven from a SPI port ( could use normal IO but a hardware SPI port will usually be faster) - clock 16 bits of data into the registers to set up the required value on the display databus, then twiddle the LCD CS/WR lines to do the write. As above, if you're short of pins, you could share a pin between the shift clock and WR, and use the data out to drive the RS line, so you'd only need 4 lines in total ( clock+WR, data+RS, CS, Reset)

 

 

 

 


Click picture above for Previous

Back to Mike's Electric Stuff

Click picture above for next