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12min

LCD Interface (Atari Lynx II)

The interface from the Lynx to the LCD is fairly straight forward. If you attach a Logic Analyzer to the LCD pins HSYNC, CLK A1/2/3, DL0/1/2/3 and VSYNC you can see the full screen data.

Probing Atari Lynx II LCD
Probing Atari Lynx II LCD
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Turning on the console and capturing you can see a few full frames of data here (shown by VSYNC below with 3 pulses for 3 full frames).

Atari Lynx II LCD Interface Overview
Atari Lynx II LCD Interface Overview
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Frame Data

If we zoom in to a single full frame (one complete image on screen) we can see there are just over 100 HSYNC pulses (for the 102 lines of a Lynx screen image).

Atari Lynx II Full Frame
Atari Lynx II Full Frame
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To find the first line (the first HSYNC pulse) listen out for the low side of the VSYNC pulse, and then skip the next high pulse, and the high pulse after is line 1.

Atari Lynx II Start Frame
Atari Lynx II Start Frame
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Notice there is a HSYNC pulse that rises just before VSYNC falls, and falls right after VSYNC does. If you are counting high pulses from HSYNC this isn't a problem, but if you are counting low pulses you will catch this pulse and possibly miss the last line due to counting one early.

Atari Lynx II HSYNC / VSYNC Overlap
Atari Lynx II HSYNC / VSYNC Overlap
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Once we have established finding line 1, all you do now is read the next 102 lines (HSYNC pulses high) to get the 102 lines of information.

The frames are 75Hz, so the Lynx runs at 75Hz refresh rate, not the more standard 60Hz.

Line Data

Zoomed in to a full HSYNC pulse shows a single line.

Atari Lynx II Full Line
Atari Lynx II Full Line
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We know the Lynx has a resolution of 160 x 102 pixels, in 12bit color RGB (so 4 bits of Red, 4 of green, 4 of blue). So red can be from 0 to 15 (or 16 different tones of red). The same applies to the other colors.

The color information is stored in the DL0, DL1, DL2 and DL3 pins. The least significant bit is DL0 and the most significant bit is DL3.

Representing a full color of red (decimal 15) would be 1111, representing mid-red (12) would be 1100 where DL3 and 2 are high (1) and DL1 and 0 are low (0).

The important part is when to read the DL color information for each pixel. The data outputs left to right, starting at the top left of the screen and outputting pixel 1 at the top left first, then moves along to the right for 160 pixels, which completes a full line.

The next HSYNC pulse starts the next line down and the cycle repeats.

Pixels are clocked out in 3 parts. Red, then Green, then Blue. Once we have RGB data (12 bits) that forms one pixel, and the next clock is for the next pixels red, then green then blue and the cycle continues.

Knowing this, we need 160 pixels times 3 colors (RGB) which is 480 clocks. The clocks A1, A2 and A3 all form a single continuous clock each of 80 pulses, totalling 240 pulses.

Atari Lynx II Clocks
Atari Lynx II Clocks
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Pixel data is clocked out on both the rising and falling edge of the clocks, so that 240 pulses turns to 480 clock outs. Each clock is a red, then green, then blue and then repeating until all 160 pixels are clocked out.

The first pixel starts on the first rising edge of clock A1.

Atari Lynx II First Pixel
Atari Lynx II First Pixel
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At this time we read out the data on the DL pins to get the first pixel color information for Red.

Next the Green color for the first pixel is read on the next edge of the clock (so the falling edge in this case).

Then the Blue data is clocked out on the rising edge.

This forms the first pixel of RGB which is black.

This is the screen we are currently looking at from Batman Returns.

Atari Lynx Batman Returns
Atari Lynx Batman Returns
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And the first line top left pixels here.

Atari Lynx Batman Returns First Line
Atari Lynx Batman Returns First Line
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If we put the knowledge to use we can see the first 12 pixels are black, and the 13th pixel is the light shade of blue.

Atari Lynx Pixel Data
Atari Lynx Pixel Data
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If we highlight the clocks where the Red Green and Blue pixels are polled, and the pixel position, overlaid with binary data, and the actual pixel it represents it makes it nice and clear.

Atari Lynx Pixel Data Details
Atari Lynx Pixel Data Details
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Logic Analyzer Dumps

Using Logic 2 you can view the Batman Returns Title screen, or a few other captures for yourself.

Batman Returns Title.sal
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Batman Text.sal
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Insert Game.sal
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Updated 23 Feb 2023
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Reading Game Cartridge (Atari Lynx II)
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TABLE OF CONTENTS
Frame Data
Line Data
Logic Analyzer Dumps