Atmel AT91SAM9 Installation and operating instructions

AT91SAM9 LCD Controller
1. Scope
This application note explains how to connect the Atmel®ARM®Thumb®-based
AT91SAM9 LCD Controller to an STN or TFT display. It includes display selection
guidelines, describes the hardware and software configurations and gives perfor-
mance results and software examples.
AT91 ARM
Thumb
Microcontrollers
Application Note
6300A–ATARM–09-Jul-07

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Application Note
2. Display Overview
2.1 TFT and STN Technologies
The most commonly used display technologies are TFT (Thin Film Transistor) and STN (Super
Twisted Nematic).
STN displays use a passive matrix screen technology that has no active or controlling element
inside the display cell. Pixels are controlled by energizing the appropriate row and column drive
lines of the matrix from outside the display, resulting in a slow frame rate. STN screens have lim-
ited color range and viewing angle (~15 degrees max).
With TFT LCDs, each pixel is controlled by one to four transistors. Typically, one transistor is
used for each of the RGB color channels. Because of this direct control technique, TFT screens
are sometimes called Active-Matrix LCDs. TFT technology provides more accurate color control,
allowing it to display more colors. TFT screens also offer a wider viewing angle range (30 to 70
degrees) than the other popular types of LCDs.
2.2 Interface
The typical interface of a display is based on analog and digital inputs. The digital lines are a
data bus, a pixel clock, vertical and horizontal synchronization signals and a data enable line.
The voltage input is generally used for contrast control. The LCD Controller drives all these inter-
face lines. If more inputs are required by the display, it may be managed by PIOs (power control,
AC bias on some STN displays, backlight control, etc.)
2.3 Blanking
For the internal synchronization mechanism, the display may need some dummy data at the
beginning and/or end of a line, and at the beginning and/or end of a frame. This is called
blanking.
Display
Contrast Control
Horizontal Synchro
Vertical Synchro
Data bus
Data Enable
Pixel Clock

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Application Note
The dummy pixels/lines are not part of the frame buffer; they are managed by the LCD Control-
ler. Some delays must be introduced in vertical and horizontal timings to support it. These delays
are often described as vertical/horizontal front/back porch delays in the display datasheets.
2.4 Definitions
The following definitions and clarifications are necessary when using the LCD Controller.
• Bits per pixel (Bpp): Corresponds to the number of bits that describe the pixel color. (i.e., in
16 bits per pixel mode, each pixel can have 65536 different colors).
• Interface Width (IfWidth): Corresponds to the number of I/O data lines (data bus width) used
for the interface between the LCD controller and the display.
• Frame Rate: This parameter is given by the display datasheet (in Hz). This rate must be
respected to ensure the correct behavior of the display, thus avoiding bad image quality
(flickering).
Real image
Dummy pixel area
Horizontal Front Porch
Horizontal Back Porch
Vertical Front Porch
Vertical Back Porch
LCDVSYNC
LCDHSYNC
LCDHSYNC
LCDDOTCK
Idle lines
Vertical Back Porch
Idle lines
Vertical Front Porch
Idle pixels
Horizontal Back Porch
Idle pixels
Horizontal Front Porch

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Application Note
3. Display Selection Guide
In order to verify the compatibility of a display with the AT91SAM9 LCD Controller, a list of items
to check is given below.
3.1 Technology Type
The LCD controller supports TFT RGB (up to 16M colors), color STN (up to 4096 colors) and
Monochrome STN (up to 16 gray shades) displays. Other technologies may also be used if their
interface is compatible.
3.2 Screen Size
The screen size is fully programmable. The maximum size supported is 2048 x 2048. Most of
standard display resolution levels are compatible: VGA (640x480), QVGA (320 x 240), etc.
In STN mode, single and double scan modes are supported. For a double scan mode, the maxi-
mum size for each panel is 1024 x 2048.
3.3 Hardware Interface
The interface must be 3.3V compliant.
All the display lines should be present in the lines description list. If the display features more
lines (i.e, gate command), the LCD Controller is not able to manage them. They could be man-
aged by the PIO Controller or other peripherals (PWM, TC, etc.).
The polarity is programmable on:
LCDDOTCK: dot clock signal
LCDDEN: data enable signal
LCDVSYNC: vertical synchro signal
LCDHSYNC: horizontal synchro signal
Refer to Section 6.1 for more details on data bus connection in TFT mode.
3.4 Timings
The display size (LxH) and the frame rate are given by the display specifications.
The LCD Controller clock (LCDDOTCK) verifies the following formula:
STN Mono:
STN Color:
TFT:
LCDDOTCKfreq FrameRate DisplaySize×
IfWidth
---------------------------------------------------------------------=
LCDDOTCKfreq FrameRate DisplaySize 3××
IfWidth
-------------------------------------------------------------------------------=
LCDDOTCKfreq FrameRate DisplaySize×=

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According to the AT91SAM9 features, the maximum LCDDOTCK frequency is equal to the mas-
ter clock (in bypass mode).
The signal timings provided by the display specification must respect the timings supported by
the LCD Controller.
• Vertical pulse width from 1 to 64 lines.
• Horizontal pulse width from 1 to 64 dot clock cycles.
• Vertical Front Porch from 1 to 256 lines.
• Vertical Back Porch from 1 to 256 lines.
• Horizontal Front Porch from 1 to 2048 dot clock cycles.
• Horizontal Back Porch from 1 to 256 dot clock cycles.
Parameter Min Max Unit Symbol
Vertical Front Porch 1 256 Line T0
Vertical Back Porch 1 256 Line T1
Horizontal Front Porch 1 2048 LCDDOTCK cycle T2
Horizontal Back porch 1 256 LCDDOTCK cycle T3
Vertical Pulse Width 1 64 Line T4
Horizontal Pulse Width 1 64 LCDDOTCK cycles T5
LCDVSYNC
LCDHSYNC
LCDHSYNC
LCDDOTCK
T5
T5T2 T3T3
Horizontal BlankingActive Area
T4
T4T0 T1T1
Vertical Blanking

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Application Note
4. TFT Display Selection Guide Example
4.1 Display Description
An example of a display specification (TX09D71VM1CCA on AT91SAM9261-EK):
• TFT QVGA
• RGB 262K colors
• VCC [3.0 to 3.6V]
• Frame rate: 60 Hz
• Vertical Pulse Width : typ = 1 (in lines)
• Vertical Back Porch (VBP) : typ = 4 (in lines)
• Vertical Front Porch (VFP) : typ = 2 (in lines)
• Horizontal Pulse Width : typ = 5 (in pixels)
• Horizontal Back Porch (HBP): typ = 17 (in pixels)
• Horizontal Front Porch (HFP): typ = 11 (in pixels)
Interface:
4.2 Compatibility
To determine whether the display in the example is compatible, the following points should be
evaluated:
4.2.1 Technology
It is a TFT display, thus the technology is supported.
4.2.2 Size
QVGA is 320 x 240, thus the size is acceptable.
4.2.3 Interface
VCC = 3.3V
Data bus 18 bits, 6 bits per color.
VSYNC corresponds to LCDVSYNC
HSYNC to LCDHSYNC
Display
Vctrl
HSYNC
VSYNC
R0 - R5
DTMG
DCLK
PCI
G0 - G5
B0 - B5

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Application Note
DCLK to LCDDOTCK
DTMG to LCDDEN
Add a passive filter between LCDCC and Vctrl.
Use a PIO for PCI control.
This interface is compatible.
4.2.4 Timings
Frame rate 60 Hz:
LCDDOTCKfreq = 60 x 320 x 240 = 4.608 MHz < LCDDOTCKfreq max.
The delays are all between 1 and 17. The LCD controller is able to manage delays between 1
and 256: all the blanking delays are in a compatible range.
The timings are compatible.
4.2.5 Conclusion
The display given in the example is compatible with the AT91SAM9261 LCD Controller.
5. STN Display Selection Guide Example
5.1 Display Description
An example of a display specification (SP06Q002):
• STN QVGA
• 16 gray shades
• VCC [3.0 to 3.6V]
• Frame rate: 75 Hz
• Horizontal Pulse Width : typ = 1 (in pixels)
• Horizontal Back Porch (HBP): typ = 1 (in pixels)
• Horizontal Front Porch (HFP): typ = 1 (in pixels)
Interface:
Display
Vled-/Vled+
CL1
FLM
CL2
DOFF
D0 - D3

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Application Note
5.2 Compatibility
To determine whether the display in the example is compatible, the following points should be
evaluated:
5.2.1 Technology
It is a STN display, thus the technology is supported.
5.2.2 Size
QVGA is 320 x 240, thus the size is acceptable.
5.2.3 Interface
VCC = 3.3V
Data bus 4 bits.
FLM corresponds to LCDVSYNC
CL1 to LCDHSYNC
CL2 to LCDDOTCK
Add a passive filter between LCDCC and Vled-/leld+
Use a PIO for DOFF control.
This interface is compatible.
5.2.4 Timings
Frame rate 75 Hz:
LCDDOTCKfreq = 75 x 320 x 240 / 4 = 1.44MHz < LCDDOTCKfreq max.
The delays are all equal to 1. The LCD controller is able to manage delays between 1 and 256:
all the blanking delays are in a compatible range. In STN mode, vertical timings should be set to
0.
The timings are compatible.
5.2.5 Conclusion
The display given in the example is compatible with the AT91SAM9 LCD Controller.
6. Configuration
6.1 TFT Hardware Connection
The AT91SAM9 LCD Controller is based on Blue-Green-Red (BGR) standard while most graph-
ical layers use RGB color map.
As an example, the memory map of a pixel in 16-bit mode in the frame buffer is:
where:
I B4B3B2B1B0G4G3G2G1G0R4R3R2R1R0

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Application Note
– I is Intensity Bit
– R[4:0], G[4:0] and B[4:0] are respectively red, green and blue video components.
Most graphical layers use RGB 5-6-5:
This leads to a swap between blue and red components. There are two solutions to correct, via
software or via hardware.
6.1.1 Software Swap
The swap of blue and red components by software is CPU consuming.
This is done using a piece of code. An example of the code follows, in C for an inline function:
__inline unsigned int swap_it(swap){
unsigned int tmpR,tmpB;
tmpB = swap <<10;//extract Blue
tmpR = swap >>10;//extract Red
swap = swap & 0x83E0; //keep only Green and I Bit
return swap |= tmpB|tmpR;/returns the swapped color
}
In ASM, once compiled with armcc:
mov r0,r5
mov r3,r0,lsl #10
mov r2,r0,asr #10
ldr r1,0x000005fc ; = #0x000083e0
and r0,r0,r1
orr r1,r3,r2
orr r1,r1,r0
ARMulate gives 8 CPU cycles for this sequence.
It must be done for each pixel of the frame, i.e., 320*240 = 76,800 times for each frame. There-
fore, 76,800*8 = 614,400 CPU cycles per frame.
This means 614,400 * 25 = 15,360,000 CPU cycles per second for a 25 Hz refresh rate.
Compared to the 200,000,000 CPU cycles per second when running at 200 MHz, this gives
7.7% of the CPU time wasted to swap the LCD framebuffer.
For use the software solution, the LCD device is to be connected as follows to the PIOB lines.
6.1.1.1 18-bit TFT Display
In this mode, the LCD Controller can be programmed in 16-bit or 24-bit mode, as the LCD Con-
troller does not offer 18-bit mode.
In 16-bit mode, some framebuffer memory is saved. The number of colors available is 65,536.
R4 R3 R2 R1 R0 G5 G4 G3 G2 G1 G0 B4 B3 B2 B1 B0

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Application Note
In 24-bit mode, as only 18 bits are wired to the LCD device, the number of colors available is
262,144.
Figure 6-1. 18-bit TFT Display Hardware Connection (Software Swap) in 24-bit Mode
LCD Device
R0
R1
R2
R3
R4
R5
G0
G1
G2
G3
G4
G5
B0
B1
B2
B3
B4
B5

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Application Note
6.1.1.2 24-bit TFT Display
Figure 6-2. 24-bit TFT Display Hardware Connection (Software Swap)
LCD Device
R0
R1
R2
R3
R4
R5
R6
R7
G0
G1
G2
G3
G4
G5
G6
G7
B0
B1
B2
B3
B4
B5
B6
B7

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6.1.2 Hardware Swap
The CPU time for swapping can be reduced by the hardware solution for swapping of the red
and blue signals. The LCD device is connected as follows to the PIOB lines.
6.1.2.1 18-bit TFT Display
In this mode, the LCD Controller can be programmed in 16-bit or 24-bit mode.
In 16-bit mode, some framebuffer memory is saved. The following table explains how to connect
a 18-bit TFT display in 16-bit mode, using the RGB 6-5-6 format via the 1-5-5-5 format of the
LCD Controller. The number of colors available is 65,536.
The 5 bits for Red and Blue are connected on the MSB pins of the display. B0 and R0 are con-
nected to GND. LCDD10 and LCDD2 are not used.
MemoryBits 1514131211109876543210
RGB5-6-5 R4R3R2R1R0G5G4G3G2G1G0B4B3B2B1B0
LCD Controller
BGR Format I B4B3B2B1B0G4G3G2G1G0R4R3R2R1R0
LCD Controller
Interface D18 D23 D22 D21 D20 D19 D15 D14 D13 D12 D11 D7 D6 D5 D4 D3
DisplayInterface R5R4R3R2R1G5G4G3G2G1G0B5B4B3B2B1

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Figure 6-3. 18-bit TFT Display Hardware Connection in 16-bit Mode: RGB 5-6-5 Format
LCD Device
B0
B1
B2
B3
B4
B5
G0
G1
G2
G3
G4
G5
R0
R1
R2
R3
R4
R5

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In 24-bit mode, as only 18 bits are wired to the LCD device, the number of colors available is
262,144.
Figure 6-4. 18-bit TFT Display Hardware Connection in 24-bit Mode
LCD Device
B0
B1
B2
B3
B4
B5
G0
G1
G2
G3
G4
G5
R0
R1
R2
R3
R4
R5

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6.1.2.2 24-bit TFT Display
Figure 6-5. 24-bit TFT Display Hardware Connection in 24-bit Mode
6.2 STN Hardware Connection
STN display data bus is not based on RGB or BGR bus. It is based on data bus D0 to Dn.
Refer to the AT91SAM9 datasheet for more details.
6.3 Software
6.3.1 Initialization Sequence for AT91SAM9261 device example
6.3.1.1 Power Management
The HCLK bit of the PMC_SCER register must be set before using the LCD Controller. It
enables the LCD Controller clock. No specific peripheral clock is needed.
LCD Device
B0
B1
B2
B3
B4
B5
B6
B7
G0
G1
G2
G3
G4
G5
G6
G7
R0
R1
R2
R3
R4
R5
R6
R7

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6.3.1.2 I/O Lines
The pins used for interfacing the LCD Controller are multiplexed with PIO lines. The programmer
must first program the PIO Controller to assign the pins to their peripheral function. If some I/O
lines of the LCD Controller are not used by the application, they can be used for other purposes
by the PIO Controller.
6.3.1.3 Turn off the LCD Controller
To be sure that initialization is correct, first disable the LCD Controller and DMA by clearing the
LCD_PWR and the DMAEN bits in the PWRCON and the DMACON registers, respectively.
6.3.1.4 Palette
If the number of colors is less than or equal to 256, the palette LUT must be initialized.
6.3.1.5 LCDCON1
The LCDDOTCK is configured in the LCDCON1 register. If the LCDDOTCK frequency is equal
to the LCDC Clock frequency, the BYPASS bit must be set. If not, the CLKVAL field must be pro-
grammed as described below.
Calculate the theoretical Dot Clock:
STN Mono:
STN Color:
TFT:
Calculate the corresponding theoretical value for CLKVAL:
Round down the CLKVALtheo value to find the real CLKVAL value.
Check the LCDDOT frequency:
Example:
A TFT QVGA display has the following features: 320 x 240, 60 Hz, 262K colors, 18-bit data bus.
LCDC Clock is 100 MHz.
LCDDOTCKfreq FrameRate DisplaySize×
IfWidth
---------------------------------------------------------------------=
LCDDOTCKfreq FrameRate DisplaySize 3××
IfWidth
-------------------------------------------------------------------------------=
LCDDOTCKfreq FrameRate DisplaySize×=
CLKVALtheo LCDCClockFreq
2LCDDOTCKtheo
×()1–
--------------------------------------------------------------------=
L
CDDOTCK LCDCClock
2CLKVAL 1+()×
-------------------------------------------------=

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Application Note
LCDDOTCKtheo = 320 x 240 x 60 = 4.608 MHz
CLKVALtheo = 100 / (2 x 4.608) - 1 = 9.85
CLKVAL = 9
LCDDOTCK = 100 / (2 x (9+1)) = 5 MHz.
An STN QVGA display has the following features: 320 x 240, 75 Hz, 4-bit data bus. LCDC Clock
is 100 MHz.
LCDDOTCKtheo = 320 x 240 x 75 / 4 = 1.44 MHz
CLKVALtheo = 100 / (2 x 1.44) - 1 = 34.7
CLKVAL = 34
LCDDOTCK = 100 / (2 x (9+1)) = 1.43MHz.
6.3.1.6 LCDCON2 and LCDFRMCFG for AT91SAM9261
The display resolution is set in the LCDFRMCFG register.
The LINEVAL field corresponds to the number of lines of the display - 1.
Note that the HOZVAL field does NOT always correspond to the number of columns:
In TFT mode,
Horizontal size is n+1. The LCD Controller needs n+1 LCDDOTCK cycles to send a line. HOZ-
VAL field must be set with the value n.
In STN monochrome mode,
HOZVAL ColumnNumber 1–=
LCDHSYNC
LCDDOTCK
LCDD0
LCDD1
LCDD23
B0-0
B1-0
R7-0
B0-n
B1-n
R7-n
HOZVAL ColumnNumber
Ifwidth
------------------------------------------1–=

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Horizontal size is n+1. Interface width is m+1. The LCD Controller needs (n+1) / (m+1) LCD-
DOTCK cycles to send a line.
HOZVAL field must be set with the value .
In STN color mode,
Horizontal size is n+1. Interface width is m+1. The LCD Controller needs 3 x (n+1) / (m+1) LCD-
DOTCK cycles to send a line.
HOZVAL field must be set with the value .
The other display parameters are configured in the LCDCON2 register:
Type, Scan mode, Interface width, Pixel size, etc.
6.3.1.7 LCDCON2 and LCDFRMCFG for Other AT91SAM9 Products
The display resolution is set in the LCDFRMCFG register.
The LINEVAL field corresponds to the number of lines of the display - 1.
The LINESIZE field corresponds to the number of columns of the display - 1.
LCDHSYNC
LCDDOTCK
LCDD0
LCDD1
LCDDm
P0
P1
PnP3
Pn-1
Pn-2
n1+
m1+
--------------1–
H
OZVAL ColumnNumber 3×
Ifwidth
---------------------------------------------------- 1–=
LCDHSYNC
LCDDOTCK
LCDD0
LCDD1
LCDDm
R0
G0
Bn
LCDDm-1 Gn
n1+()3×
m1+
----------------------------1–

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Horizontal size is n+1. The LCD Controller needs n+1 LCDDOTCK cycles to send a line. LINE-
SIZE field must be set with the value n.
The other display parameters are configured in the LCDCON2 register:
Type, Scan mode, Interface width, Pixel size, etc.
6.3.1.8 Timings
The LCDHSYNC and LCDVSYNC signal pulse width are configurable through the VPW and
HPW fields in the LCDTIM1 and LCDTIM2 registers. It is defined in number of LCDDOTCK
cycles.
6.3.1.9 Blanking
Write VFP, VBP, HFP, HBP according to the data given in the display datasheet.
6.3.1.10 Interrupt
The LCD Controller interrupts are configured as the other AT91 peripherals through the
Enable/Disable/Mask/Status/Clear registers.
6.3.1.11 Contrast
The contrast PWM Signal is programmable from 0 to FF in the CVAL field of the
CONTRAST_VAL register. Polarity and frequency are also programmable in the PS and POL
fields of the CONTRAST_CTR register. To enable/disable it, set or clear the ENA bit.
6.3.1.12 DMA Base Address
In TFT and STN Single Scan mode, the frame buffer address is stored in the DMABADDR1 reg-
ister. In STN Double Scan mode, the second frame buffer address is stored in the DMABADDR2
register.
If the frame buffer is located in the SRAM memory, use the address base 0x0030 000.
If the frame buffer is located in the SDRAM, it is recommended to store it in a different bank than
the application in order to optimize the SDRAM access. Refer to the Atmel application
note”Using the SDRAM on AT91SAM9 Microcontrollers”, ref. 6256, for more details.
6.3.1.13 DMA Frame Configuration
Two parameters are needed to configure the DMA: the burst length and the frame size.
BRSTLN = burst length - 1
FRMSIZE = DisplaySize x Bpp / 32
Note that the Bpp parameter to use is the one used for the LCD Controller configuration. If it is
an 18-bit display, the configuration is 16 bits or 24 bits. In this formula, Bpp is 16 or 24, not 18.
6.3.1.14 FIFO
The FIFOTH field must be programmed with:
FIFOTH = 512 - (2 x DMA_BURST_LENGTH + 3)
where:
DMA_BURST_LENGTH is defined in the DMAFRMCFG register

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6.3.1.15 DMA Enable
Reset and enable the DMA by setting the DMARST and DMAEN bits in the DMACON register. It
must be done in 2 steps.
6.3.1.16 LCD Enable
Enable the LCD Controller by setting the LCD_PWR bit in the PWRCON register. At this
moment, the LCD Controller is running and is sending frames to the displays via the LCD Con-
troller interface. Depending on the display interface, other IOs may be configured to enable the
display, or for backlight activation.
6.3.2 Software Examples
The AT91SAM9261-BasicLCD-IAR_4_41 Project configures:
A monochrome STN display, 320 x 240, 16 gray shades
A Color STN display, 320 x 240, 4096 colors
A TFT display, 320 x 240, 16M colors
7. Performances
7.1 Matrix Configuration
In order to set the maximum priority for the LCD Controller (display frame rate is more important
than application performance), it is recommended to set the slave where the frame buffer is
stored with the following configuration: LCD as a Fixed default Master.
7.2 Bus Bandwidth
7.2.1 Application in SDRAM, Frame Buffer in SDRAM
The Matrix has to share the SDRAM access between the ARM Core and the LCD Controller.
The effect on the application performance depends on the LCD throughput. The throughput is
the product of the frame rate multiplied by the display size and the number of bits per pixel.
Section 7.2.5 gives details on the impact on the performances of different LCD configurations.
7.2.2 Application in SRAM, Frame Buffer in SDRAM
Thanks to the multi-layer feature of the matrix, transfers can be done in parallel between SRAM
and the ARM Core for the application, and between SDRAM and the LCD Controller for the
frame buffer. Thus, application performances are not affected by the LCD.
7.2.3 Application in SDRAM, Frame Buffer in SRAM
Thanks to the multi-layer feature of the matrix, transfer can be done in parallel between SDRAM
and the ARM Core for the application, and between SRAM and the LCD Controller for the frame
buffer. Thus, application performances are not affected by the LCD.
7.2.4 Application in SRAM, Frame Buffer in SRAM
The matrix has to share the SRAM access between the ARM Core and the LCD Controller. The
effect on the application performance depends on the LCD throughput. The throughput is the
product of the frame rate multiplied by the display size and the number of bits per pixel.
Section 7.2.5 gives details on the impact on the performances of different LCD configurations