Archive for May 4th, 2015

HP 7475A Plotter: Serial Cable for Hardware Handshaking

The HP 7475A wakes up with hardware handshaking enabled: DTR starts high and goes low when the internal 1 KB buffer has less than 80 bytes remaining. The plotter also supports XON/XOFF handshaking, a sad software thing you’d use only if you had no other choice.

The Chiplotle doc provides a wiring diagram for a suitable 9-to-25 pin cable, so I printed one and doodled on it while pondering the Great Cable Stash:

HP7475A Plotter - Serial Cable

HP7475A Plotter – Serial Cable

The color codes over on the left of the top diagram match a prebuilt cable I hoped to repurpose, but it had only five conductors, none of which were DSR or CTS. Pfui!

So I used a hank of gorgeous flexy 9-conductor cable (which came with premolded DE-9 ends of the wrong gender, now amputated into pigtails and back in the GCS), which supported the connections redrawn on the bottom in proper numeric order, used the obvious color sequence (Bn R O Y G Bl V W K), then soldered suitable connectors on each end:

HP 7475A Plotter - serial cable

HP 7475A Plotter – serial cable

And it worked the first time…

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