HP7475A Plotter - Serial Port DTR Handshaking

Shows the DTR pin blinking to control serial data going to the HP7475A plotter's buffer, driven by a hacked version of the Chiplotle plotter driver.

The pin names give the plotter's point of view: RD from the PC and DTR to the PC. For reasons lost to history, the small arrows on the handmade label point in the wrong direction.

The standard Chiplotle handshaking function introduces pauses when it asks the plotter to return the available buffer space. Removing that query and enabling hardware handshaking allows the plotter to run at full speed.

More info on my blog:

The plotter sounds exactly like you'd expect from the audio track...