As I understand it, Serial Port 3 (the optional Audio Cassette Interface) doesn't support hardware handshaking via RTS/CTS. That being the case, how does a device like a high-speed paper tape punch/reader (shown in the latest video) connected to Serial Port 3 manage to tell the Altair when it has a byte to send (from its reader) or is ready to receive a byte (to punch)? Is it just that the Altair is always keeping ahead of the tape punch/reader so it never needs the device to pause? Presumably in the video demo of a high-speed tape punch/reader the baud rate on Serial Port 3 was set much higher than 300 baud, since the point of the demo is to show how much faster than cassette the fast paper tape is.
Sorry if these are naive questions. All I really need to know is what settings to use on the Serial Port 3 to work with a GNT-4604; the rest of the above is just me trying to make sense of what's going on!
Gabriel Egan