I have it all worked out and tested. It was a parallel IO board using an 8255A, with TTL signals driving the two stepper motors and pen solenoid. TTL 5V signal to one of the four poles of the uniphase stepper motors moves it 3.6 degrees, the operator buttons are reported as inverted TTL signals, no protocols or intelligence at all in the plotter so my job was dead simple. The 20 wire ribbon cable is the six button inputs, the eight stepper motor outputs and the pen solenoid output, plus a ground return. The operator buttons, for example to move the pen to the right, are sent to the computer whose driver would have to step the motor, rather than occurring locally in the plotter. Did I mention that it had zero digital logic chips or intelligence? Nine transistor drivers, a power supply and a few pullup and current limiting resistors, plus the steppers, solenoid, switches and buttons. If anyone else ever needs one, I have documented the cable assignments here so that they are searchable on the web. I will also mention the S-100 bus card assignments to the 8255A ports in case someone wants to use it with a retro machine through the interface card. Pins 1, 2, 4 and 5 are not connected. Pin 3 is ground Pin 6 is inverted TTL input, status of the "start/enter" button on the cover, port PA5 Pin 7 is the central "fast" button for pen movement, inverted TTL input, port PA4 Pin 8 is the "pen right" button, inverted TT input L, port PA3 Pin 9 is the "pen left" button, inverted TTL input, port PA2 Pin 10 is the "pen down" (actually rotate drum and paper up) button, inverted TTL, port PA1 Pin 11 is the "pen up" button, inverted TTL input, port PA0 Pin 12 is the output to activate the pen solenoid so that the pen is marking the paper, TTL 5V to activate, port PB4 Pin 13 is the output for one pole of the drum movement stepper motor, TTL 5V on this and 0 on the other three, port PC3 Pin 14 is the output for a second pole of the drum movement stepper motor, TTL 5V activates, port PC2 Pin 15 is the output for a third pole of the drum movement stepper motor, TTL 5V activates, port PC1 Pin 16 is the output for a fourth pole of the drum movement stepper motor, TTL 5V activates, port PC0 Pin 13 is the output for one pole of the pen left-right movement stepper motor, TTL 5V on this and 0 on the other three, port PB3 Pin 14 is the output for a second pole of the pen left-right movement stepper motor, TTL 5V activates, port PB2 Pin 15 is the output for a third pole of the pen left-right movement stepper motor, TTL 5V activates, port PB1 Pin 16 is the output for a fourth pole of the pen left-right movement stepper motor, TTL 5V activates, port PB0 For those not familiar with stepper motors, they have four poles each with a ring of 25 'teeth' that will attract a permanent magnet on the rotor. The four rings are staggered so that in total there are 100 positions around the dial - 3.6 degrees per step. Energize one pole and the magnet is held to the nearest tooth of that pole. Drop that pole and activate another whose tooth is adjacent and the rotor swings one position to hold at the tooth on that pole ring. Interface is a simple four bit circular shift register with one high and three low bits circulating in the pattern. Shift it once and the motor moves one step in the associated direction. Carl ________________________________ This e-mail message, including any attachments, is for the sole use of the person to whom it has been sent, and may contain information that is confidential or legally protected. If you are not the intended recipient or have received this message in error, you are not authorized to copy, distribute, or otherwise use this message or its attachments. Please notify the sender immediately by return e-mail and permanently delete this message and any attachments. Gartner makes no warranty that this e-mail is error or virus free.