I'd say the math is wrong on both sides. :)
IIRC, his drum is around 6.5" diameter, to achieve 20.48 inches circumference. He is generating 20480 bits per revolution, giving the 1000 bits per inch.
The drum is rotating 6 times per second, so 6 ∗ 20480 = 122880 bits per second. Somewhere in the earlier discussion, I think I saw that he is using 1 byte per bit (??? presumably to save the bit-shifting circuitry?), so that would work out to 122880 bytes/second. If he is using bit-shifting circuitry, so that each byte is 8 bits, then he can reduce that to 15360 bytes per second.
Either way, it is a long way from 625000 bytes per second!!
--- In Homebrew_PCBs@yahoogroups.com, "cunningfellow" <andrewm1973@...> wrote:
>
> > Joh Elson wrote:
> >
> > Note that my photoplotter as it is cranks
> > out a pixel every 5 us, so even as 8-bit
> > bytes, that is 625,000 bytes a second.
>
> 16.384" drum
> 1000 dpi
> 600 RPM (10 r/s)
> 1 bit per pixel
> 8 bits per byte
>
> I get 20 kilobyte per second
>
> Am I missing something
>