The Buttons

The Buttons

On this page:

• Basics
• Protocol UART Buttons
  • Initialization
  • Button Codes
  • Power Off
• Testing The Buttons

Basics

The state of the buttons and the scrollwheel is communicated via the button UART. (See pinouts.) To initialize the buttons a certain sequence of bytes is sent to the front panel. After that the panel sends bytes which encode the current button and scrollwheel state in regular intervals.
The interface settings are as follows:

baudrate	bits	paritybit	stopbits
38400	8	even	1

With these parameters it is possible to communicate with the "button part" of the display with an microcontroller or with a PC.

Protocol UART Buttons

Initialization

To initialize the "button part" of the front panel a sequence of bytes is sent to the frontpanel via the button UART. The bytes are sent two bytes at a time, so one command seems to consist of two bytes. The panel acknowledges each sent pair with "0x02".
If the buttons are not initialized the state of the buttons is communicated nevertheless but does not include the state of the scrollwheel.
The bytes are as follows:

command nr.	bytes	meaning
1	0xFE 0xDC	reset UART communication
2	0x02 0x20	?
3	0x0E 0xFF	?
4	0x0F 0xFF	?
5	0x0D 0x00	?
6	0x0C 0x1F	?
7	0x03 0x01	?
8	0x0A 0x19	?
9	0x0A 0x11	Scrollwheel on
10	0x0B 0x05	Set frequency with which the state of the buttons is sent
11	0x02 0x20	?
12	0x0E 0xFF	?

Button Codes

The front panel sends two bytes over the button-UART in intervals to communicate the state of the buttons and scrollwheel. Byte 1 expresses the state of the buttons, byte 2 the state of the scrollwheel.

pressed button	byte 1 (hex)
none	0xC0
down	0xC1
left	0xC2
gray "diamond"	0xC9
up	0xCA
plus	0xD1
navi	0xD2
minus	0xD9
OK	0xDA
gray "diamond"	0xF1
Home	0xF2
screenkey right	0xF9
screenkey left	0xFA
right	0xE9
back	0xEA

The scrollwheel position seems to use a counter that overflows after 64 steps.

scrollwheel position	byte 2 (hex)
0	0x80
...	...
63	0xBF

As can be seen it can be easily distinguished between byte 1 and 2 ( Byte 1 is always >=0xC0, Byte 2<=0xBF )

Power Off

Before power off 0x0E 0xFF 0x0A 0x00 0x00 is sent to the front panel.

Testing The Buttons

To use the buttons 3,3 V is connected to the "power" and "reset" pins, surprisingly GND is connected to ground. ;) After that the following byte sequence is sent to the display as explained above:

0xFE 0xDC 0x02 0x20 0x0E 0xFF 0x0F 0xFF 0x0D 0x00 0x0C 0x1F 0x03 0x01 0x0A 0x19 0x0A 0x11 0x0B 0x05 0x02 0x20 0x0E 0xFF

Every pair of bytes is acknowledge with 0x20 via UART. After that the current button and scrollwheel state can be determined using the table above and the bytes that the panel is sending over UART.