let's talk about how the Vectrex renders text. 🧵 
so the ships (and the player) are created by painting lines directly from point to point. this is a *vector* display system. the vectrex aims, then turns on the electron beam, sweeps out the line, then shuts off the beam. it's like a pen plotter.
but the text is another matter. it looks a little different...
if i tweak the settings on my oscilloscope i can zoom in -- and it's a *raster* scan! text on the Vectrex is raster, while geometry is vector.
the key is to use the X and Y deflection signals to create a bunch of parallel lines. then the Vectrex gates the beam on and off to create pixels.
but there's something funny going on. i'm not seeing a normal horizontal retrace -- there should be faint diagonal lines connecting each parallel line
here's the raw X (top) and Y (bottom) signals. notice that for every Y step, the X goes up and then back? the retrace happens before the Y axis goes to the next line.
let's take a closer look at the X axis. bottom trace is the DAC output before the integrator. this output sets the *slope* of the line. all the CPU has to do is write to the DAC once and then it can transmit the characters a pixel at a time.
i've added in a little bit of the blanking signal so you can see the pixels as bright dots on the upward slope.
if i change my scope's horizontal period and zoom out, the pixels squish together and now you can read it!
now there's something else odd with the blanking signal (middle). it comes from the 65c22 VIA chip. the chip select signal for that is on the bottom, and it's not being selected for every pixel. what gives?
the blanking signal comes from the CB2 pin of the 65c22, which is a shift register! essentially the Vectrex uses the serial port to clock out pixels.
