LEM1802 Display

Built in font

The LEM1802 (LEM stands for "Low Energy Monitor") is a 128x96 pixel color display compatible with the DCPU-16. It was developed and manufactured by Nya Elektriska, and is fully backwards compatible with the LEM1801. The display is made up of 32x12 16 bit cells. Each cell displays one monochrome 4x8 pixel character out of 128 available. Each cell has its own foreground and background color out of a palette of 16 colors.

Hardware info

Name	LEM1802
ID	0x7349f615
Version	0x1802
Manufacturer	0x1c6c8b36 (NYA_ELEKTRISKA)
Colors	4,096 (RGB, 4 bits per channel)
Palette size	16 different colors

Interrupts

A	Name	Behavior
0	MEM_MAP_SCREEN	Reads the B register, and maps the video RAM to DCPU-16 RAM starting at address B. See below for a description of video RAM. If B is 0, the screen is disconnected. When the screen goes from 0 to any other value, the the LEM1802 takes about one second to start up. Other interrupts sent during this time are still processed.
1	MEM_MAP_FONT	Reads the B register, and maps the font RAM to DCPU-16 RAM starting at address B. See below for a description of font RAM. If B is 0, the default font is used instead.
2	MEM_MAP_PALETTE	Reads the B register, and maps the color palette RAM to DCPU-16 RAM starting at address B. See below for a description of color palette RAM. If B is 0, the default color palette is used instead.
3	SET_BORDER_COLOR	Reads the B register, and sets the border color to palette index B&0xF
4	MEM_DUMP_FONT	Reads the B register, and writes the default font data to DCPU-16 RAM starting at address B. Halts the DCPU-16 for 256 cycles
5	MEM_DUMP_PALETTE	Reads the B register, and writes the default color palette data to DCPU-16 RAM starting at address B. Halts the DCPU-16 for 16 cycles

Video RAM

The LEM1802 has no internal video RAM, but rather relies on being assigned an area of the DCPU-16 RAM. The size of this area is 386 words, and is made up of 32x12 cells of the following bit format (in LSB-0):

   ffffbbbbBccccccc

The lowest 7 bits (ccccccc) select define the character to display. ffff and bbbb select which foreground and background color to use. If B (bit 7) is set, the character color will blink slowly.

Palette

The display can store 16 different colors in its palette. It has a built in palette but it is also customizable. A 16 word region can be mapped to the display with one word per palette entry. Each palette entry has the following bit format:

   0000rrrrggggbbbb

where r is red, g is green and b is blue. Higher values mean lighter colors. So for example 0000-1111-1111-1111 would be white.

Value		Palette entry	RGB hex	Result
Hex	Bin
0	0000	0x0000	#000000
1	0001	0x000a	#0000aa
2	0010	0x00a0	#00aa00
3	0011	0x00aa	#00aaaa
4	0100	0x0a00	#aa0000
5	0101	0x0a0a	#aa00aa
6	0110	0x0a50	#aa5500
7	0111	0x0aaa	#aaaaaa

Value		Palette entry	RGB hex	Result
Hex	Bin
8	1000	0x0555	#555555
9	1001	0x055f	#5555ff
a	1010	0x05f5	#55ff55
b	1011	0x05ff	#55ffff
c	1100	0x0f55	#ff55555
d	1101	0x0f5f	#ff55ff
e	1110	0x0ff5	#ffff55
f	1111	0x0fff	#ffffff

Font

The LEM1802 also features a built in font, shown above. The font contains 128 characters, all of which can be customized.

As every character bitmap contains two words, mapping all characters requires a 256-word space. In each character bitmap, bits can be set to indicate the foreground color, or cleared to indicate the background. The bits are counted from the bottom-left to the top. For example, a capital E would look like this on the screen:

0000
1110
1000
1000
1100
1000
1000
1110

Note the room left on the top and side for spacing between the characters. In bitmap data for this would be:

word1: 11111110 10010010
word2: 10000010 00000000

External Links and References

• Official specification document: http://dcpu.com/monitor/