Using the Siemens S65 – Display

Using the Siemens S65 – Display
by Christian Kranz, October 2005
( )
( PDF by Benjamin Metz, 01 November 2005 )
About the Display:
Siemens used for the mobile phones S65, M65, CX65 and SK65 a 16-bit color
TFT display with 132x176 pixel. This display has integrated white backlight
LED's and an attractive screen size.
The display is available for less than 20 EUR in phone part shops and ebay.
The following picture compares the well known Nokia 6100 display with the
S65 - display.
Info: Currently there are three different display types known.
Hitachi HD66773
Epson L2F50..
The picture below shows the dimensions of the display.
The following pages describe how to use this display in own applications.
Actually it is focused on the ATMEL® AVR processor but from the description
it should be possible to use it with other controller also.
The Display pin description can be found on this Picture:
The schematic of the testboard is shown in the picture below. Both display
supplies are connected to a 2.9V supply that is generated out of an LDO from
the 5.0V supply of the ATMEL® AVR µC. I used the IRU1205CLTR LDO because I
will later need the power on/off feature of this LDO. The ATMEL® AVR µC is
running with 16MHz.
The five interface lines between the display and the µC are level-shifted from
the 5V domain of the µC to the 2.9V domain of the display. Because the
interface will run with 8MHz the impedance has to be low to get stable signals.
It might be a good idea to go to active level shifter in future to save power,
especially for the RESET line because this line has to be high as long as the
display is used. On the other hand you can use a higher impedance level shifter
here because speed is not important.
Display Backlight:
The display forward voltage was measured at one part to be 10.4V at 20mA
current. That means a relative large voltage is needed. This voltage can be
easily generated with a PWM signal generator of the µC. (Do not forget to switch
on the current limitation of your power supply until the PWM generator is
running correct. If you drive the n-channel gate high for a longer time you will
have a short circuit.) For the circuit below you need a pulse width (high/period)
of 47% at a period frequency of 62.5kHz to generate the required voltage with
15mA LED current. A block capacitor is already implemented on the display and
is not needed. You can adjust the brightness of the display by varying the OCRn
value. No software interaction is needed to generate this waveform with AVR
processor. The code example below for the ATmega128 uses timer 2 with OC2
(PB7) for PWM generation. That means you can not use PB7 for LCD_RS any
more (as in the circuit above). LCD_RS can be changed to PB5 for example.
For the final running application an over voltage protection is not required. But
during testing and development it is not a bad idea to add a protection device.
That might protect the circuit against hardware/software malfunctions.
PWM Programming example ATmega128 (AVR)
// backlight PWM generation
// use timer 2 in fast PWM mode for this
PORTB &= ~_BV(PB7); // clear port before enable
DDRB |= _BV(PB7); // will be used for OC2, must be output
TCCR2 = _BV(WGM21) | _BV(WGM20) | _BV(COM21) | _BV(CS20);
I) LS020 - Display:
Software - (Commands and Data):
Data and commands to the display controller are distinguished by the RS line. If
RS is high, the controller expects commands, if the RS line is low it expects
RS = high
RS = low
Initialization Commands:
A LCD TFT display is programmed in three steps. To switch on the display a
initialization sequence is needed to program the power chip of the display.
That is needed because of the high multiplex rate of the display a relative high
voltage is used for driving the glass. The glass voltage can be in the 10V to 20V
range and is usually generated by charge pumps.
After switching on the power usually the display parameter are programmed.
In some cases also the boost circuit has to be reprogrammed from startup to
active. After startup the display can be used for displaying...
The originally measured seven initialization sequences from the S65 display can
luckily be reduced to three sequences. In addition we do not need the very long
time intervals Siemens used in here approach. The first (of the three) used
initialization sequence is:
INIT1: (Display Software Reset)
It looks like this sequence starts the display controller. After a certain time
(min. 50ms) the second init command sequence is transmitted to the display.
0xEE04, 0x1B04
0xEF90, 0x4A04, 0x7F3F, 0xEE04, 0x4306
After that we need to wait for the display internal voltage settling.
This wait time is very sensitive. If the time is too short or too long the
display will not work! It was measured to be 7ms and this value shall also be
used to drive the display with the sequences shown here.
The second sequence follows directly and is:
0x0983, 0x0800, 0x0BAF, 0x0A00, 0x0500, 0x0600, 0x0700
After the initialization sequence the display is ready to use. An immediate clear
screen is recommended because the display shows random content after first
power on.
Power Down Commands:
For a regular shutdown a display needs normally a power down sequence to
discharge the glass voltage in a controlled manner. Otherwise the lifetime of the
display might be reduced. Currently the power down sequence is not known.
Therefore we only have the possibility to reset the display and switch off the
power supply.
Writing Full-Screen and Screen Sections:
After the initialization the display is ready to use. Usually the first thing to do is
to clear the display. That can be perfectly done with the following memory write
0xEF90, 0x05OR, 0x06YS, 0x07XS
After this command the display data can be written pixel by pixel, each
pixel 16-bit.
The parameter XS and YS are defining subsections of the display memory.
It is not required to write the complete memory. If only a part of the display
should be written the data write can be stopped and the next MEMWR
command resets the write pointer to the given coordinates.
The complete screen is written with XS = 0 and YS = 0. In that case it is not
required to repeat the command for each screen write. It is sufficient to write
simple the data again and again. The display memory is organized according the
picture on the right side. The total number of bytes is 132 x 176 x 2, that
means in total 0xB580 pixel.
The memory is written first in X - direction and second in Y - direction.
The parameter OR defines the display orientation.
OR = 0x04 sets the 0 degree orientation shown in the picture below.
OR = 0x00 defines the 90 degree orientation.
For details see the section partial screen write.
With OR = 0x04 the memory is written in X-direction, that means line by line in
X-direction from left (low X-number) to right (high X-number).
With OR = 0x00 the display memory is written in Y-direction, that means from
column by column from YS to 131.
Pixel Color Coding:
The display memory is initialized to work according the -5-6-5- color coding
(-R-G-B-) scheme. That means the first (MSB first) 5-bits are coding the
intensity of red, the following 6-bits are coding the intensity of green and the
last 5-bits the intensity of blue. (0xFFFF is white, 0x0000 is black)
Partial Screen Write:
The display memory is organized in a matrix form with X- and Y coordinates.
At each matrix coordinate one 16-bit color value (pixel) is stored.
(Advanced techniques like PET (sub-pixel addressing) seems not to be
The following picture shows the principle:
For partial writing to the memory the commands below are used. The start
corner (X1,Y1) and the end corner (X2,Y2) have to be defined. X2 has to be
larger or equal X1, Y2 has to be larger or equal Y1.
PMEMWRX: (X-direction)
0xEF90, 0x0504, 0x08X1, 0x09X2, 0x0AY1, 0x0BY2
PMEMWRY: (Y-direction)
0xEF90, 0x0500, 0x08X1, 0x09X2, 0x0AY1, 0x0BY2
The display memory can be written in X- or Y-direction. Other advanced
memory access modes are not supported.
Writing in Y-direction is usually prefered if the display is used 90-degree
rotated. If than the X- and Y-values in the PMEMWRY command are exchanged,
the coordination system - shown in the left picture is obtained. In this case
bitmaps are drawn from the upper left corner down to the lower right corner.
II) LPH - Display:
Description of init sequence not ready yet. Please look at the example code on:
( )
Power Down:
III) L2F50 - Display:
Currently two different drawing modes are known. The normal mode and
180degree rotated mode. The graphic modes are programmed using the
parameter of the DATCTL command.
Not all parameter bit combinations are known today. The next table shows the
meaning of known bits.
C1 / C2
no influence
if set memory not written
00 = not working
01 = different color coding
10 = not working
11 = 5-6-5 color coding (16-bit)
0 = normal mode
1 = 180 deg. mode
Writing in the different graphic modes is shown in the following figure.
In normal mode the (0,0) point is in the left upper corner.
The (X,Y) coordinates for the SD_CSET and SD_PSET commands are given in
natural order. (X1,Y1) is the upper left corner, (X2,Y2) is the lower right corner.
In 180 degree mode things are a little bit more confusing. The Y-axis changes
the direction, but X-axis not. In addition, if a rectangular area is drawn, (X1,Y1)
is now the lower right corner of the rectangle and (X2,Y2) is the upper left
corner, but still X1 has to be lower than X2 and Y1 has to be lower than Y2.
That means if e.g. X1=0 and X2=15 the rectangular is drawn from starting at
X=15 with the first bit. Then it is drawn down to X=0 ending with the 16'th bit.
Power Down:
0x8E00 - Command
Reengineering the S65 Display:
The Siemens S65 display is a special manufacturing for the Siemens AG (now
Siemens/BenQ). Because of that it is very difficult to get data sheets for the
used display controller. The display is a product of Seiko-Epson but does not
response to the known Epson display commands (also not to the commands of
relative new Epson 16-bit controller). Because of that I decided to do a reengineering of the display interface using a S65 mobile phone.
It was easy to figure out that Siemens uses a serial two wire interface with
additional chip select, a command/data signal (usually called RS) and a reset
signal. The clock frequency of the serial interface is 13MHz. Supply voltages are
2.9V for the display driver and 1.8V for the digital interface. In addition there
are two supply pins for the four white backlight LED's. The LED's are serial
connected and buffered with a capacitance on the display board. The serial
connection ensures a very constant light intensity distribution. That is because
each LED is driven by the same current. The disadvantage is that a relative high
voltage is needed for driving the LED’s. The LED voltage was measured to 10.4V
at 20mA for one display. But in the hardware section you can see that it is not
very difficult to generate the voltage with a PWM signal generated by the µC.
The display pin out can be seen on the figure on the left side. CS is the chip
select line, CLK the clock line, DAT the data line, RS the command/data
identification, 2V9 the 2.9V supply, 1V8 the 1.8V supply, LED+ the positive LED
supply and LED_GND the negative LED supply.
The display interface was measured using a HP (Agilent) 16-channel digital
oscilloscope. (unfortunately a logic analyser was not available)
The display commands and data are written in a 16-bit format like the example
on the picture. A data bit is latched with the rising edge of the clock signal by
the display controller.
Start Up Sequence:
The following sequences for starting the display could be identified:
Sequence 1: (time 0ms)
Sequence 2: (time 68ms after start)
0xEF00, 0xEE04, 0x1B04, 0xFEFE, 0xFEFE
0xEF90, 0x4A04, 0x7F3F, 0xEE04, 0x4306
Sequence 3: (time 75ms after start)
0x0983, 0x0800, 0x0BAF, 0x0A00, 0x0500, 0x0600, 0x0700
Sequence 4: (time 182ms after start)
Sequence 5: (time 297ms after start)
Sequence 6: (time 401ms after start)
Sequence 7: (time 460ms after start)
In addition it could be measured, that Siemens always refreshes the screen
at once. That means also if only parts of the screen are changed the complete
display memory is refreshed. Reason for that is, that Siemens uses an display
graphic controller like the s1d13732. This controller holds the display memory
and writes the display content via hardware.
Only the commands are generated by the µC. The sequence used by Siemens
for writing the compete display is:
write complete display memory:
0xEF90, 0x0500, 0x0600, 0x0700
After that the display data follows (with RS line low). Writing the display data
takes 28.59ms which corresponds to (132*176*16=371712 bits with 13MHz
clock frequency.
Power Down Sequence:
Unfortunately the power down sequence could not be measured with the used
equipment. It was not possible to find a proper trigger condition to get a reliable
repeatable measurement of the power down sequence.
Triggering to the backlight was possible but the memory of the digital scope was
to small to catch the sequences. Unfortunately the backlight is switched off after
the display is powered down. Spending more effort it might be possible to catch
the power down sequence but that is not done up to now. The proposed
sequence so far is reset of display and switching off the supply.