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!!
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
>