Re: [midatlanticretro] IMSAI to make the same music an Altair can?
- On 5/24/11 9:25 AM, B Degnan wrote:
> I thought that the interference came from the front panel or theIt comes from just about everything, and the noise coming out of the
> processor cards, at least with the Altair anyway.
radio is a blend of it all, including byproducts of constructive and
destructive interference between RFI emitted by the various subsystems
in the machine.
In the common PDP-8/e music program, memory access patterns in
particular are varied in software to produce the musical AM
interference. This is because the interference generated by the
magnetic core memory's X/Y drivers is strong enough to essentially drown
out everything else. Those drivers push relatively large currents
through the X/Y core select lines, at least compared to the signals
flowing around in the rest of the system. (that's why core memory runs
Front panels also tend to be good emitters because the current
required to drive those early LEDs, usually 10mA-25mA, is much higher
than typical logic signals.
Port Charlotte, FL