Retro Computer Laboratory

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====== Whirlwind I Vector Interface ======

This is a preliminary text.

See also my  [[https://media.ccc.de/v/vcfb2023_-_181_-_de_-_202310141130_-_vektorgrafik_hardware_fuer_eine_whirlwind_simulation_auf_einem_raspberry_pi_-_rainer_glaschick|presentation on the VCFB 2023]]

===== Introduction =====


To connect a Whirlwind I (WWI) machine (emulated or simulated) to a physical CRT
not in raster, but in X-Y-Z-mode,
a hardware interface supports drawing of vectors.
Single points are drawn as zero-length vectors.

The board has a dual 12-Bit D/A converter (MCP 4822) controlled by SPI,
and two digital inputs to set the starting point and to draw a (short) vector
with a given velocity. 

As a vector is drawn by setting the direction and velocity,
the destination point is not defined by its absoulte coordinates.
Although the analog hardware is quite precise, 
the vector size is limited to a fraction of the sceen.
Thus, long vectors must be composed from shorter ones, 
as to restart at a known location.  

The board can handle two CRT's and lightguns.

The design was inspired by the Vectrex game console, 
but allows to set a starting point directly. 

==== Design ====

The interface is essentially an settable integrator 
for X and Y deflection voltages.
The output of the board provides &plusmn;2.5V on its (analog) output.

Normal use is as follows:
- Transmit x and y coordinates of the starting point via SPI to the A/D converter
- Strobe the 'doMOVE' signal to set initial values of the integrators
- Transmit x and y values for the speed via SPI
- Strobe the 'doDRAW' signal to draw the vector with the actually set speed

==== References ====

[[https://github.com/raigl/WWI-vecIF]]