Finished work on System Source Museum 1053 console printer

TEDIUM PAYS OFF EVENTUALLY - THE TYPEWRITER WORKS WELL

After I exited the loop of adjustments when all character positions were selecting properly in both upper and lower case hemispheres of the type element, I had just one final area to tune up. The 1053 has microswitches at key points in the mechanism to provide feedback to the controller logic inside the IBM 1130 system. These have to be set to fairly exacting points of the mechanical movement, otherwise the controller might start another character print or movement when the typewriter is not in a good position to accommodate it. 

One set are meant to protect the typewriter during 'long' operations. These are movements that take a variable amount of time to complete and are much longer than a single print or shift cycle. For instance, the time for a Tab movement to finish depends on which column we start from and how far away is the next column with a tab set. Similarly, carrier return time depends on how far to the right we were when it is started. 

The other inform the controller when the rotation of the mechanism is at a sensitive point where further commands shouldn't be attempted and then when the mechanism reaches a point where it could again accept requests. Typing a single character involves starting the print cycle from a standing start, moving the type ball and then coming to a stop. 

It is possible to stream an additional character before the print cycle stops, so that the clutch never stops it. The mechanism just continues around in another cycle. This allows the typewriter to reach its maximum speed of just over 15 characters per second, as it is considerably slower if it has to start and stop for each printed character. 

Shifting between upper and lower hemispheres consumes one print cycle, so the actual max printing speed also depends on the specific characters being typed - at worst case it will only print a bit less than 8 characters a second (if a shift is needed between each character). 

I was finally satisfied with its behavior and performance. I put the covers back on and wrapped it up, ready to be brought back to Maryland and enjoyed by museum visitors. 

PRINTER ADJUSTMENTS ARE FINALIZED, READY TO SEND THE UNIT BACK

I was happy to call them and let them know the console printer is ready for pickup. They can get their 1130 back in operation soon. The pickup is this Friday. 

ALSO LOANING A 1053 SIMULATOR FOR TIMES WHEN THE PRINTER FAILS

I designed and built a simulator that plugs into the IBM 1130 and replaces the connections to the 1053 console printer. It delivers the output of the printer over a USB serial link to a terminal or computer where the same results will be seen as would be printed on paper by the printer. 

It provides the same ability to set tab positions, left and right margins, offers a display of the current print column along the line, offers the same return, tab and space buttons for manual interaction, and displays the full character set in both red and black ink. 

It had been initially built with relay boards driven by an Arduino Mega 2560 to provide the feedback signals to the 1130, but the performance of the relays was not sufficient to meet the signal timing produced by the I/O Selectric printer mechanism. With each print cycle taking about 65 milliseconds, the -TWR CB RESPONSE signal would need to drop from 48V to 0 at 7.22 ms into the cycle and return back to 48V by the 43 ms point. 

The relay boards I initially used require up to 15ms to turn on and up to 10ms to turn off. That would have delayed the signal above until 22 ms into the print cycle, way past the safe point where further commands could be issued. Further, it would remain off until 53 ms. Generally these are acceptable for switching rates up to 10 per second, but the 1053 can exceed 15 cycles per second. 

Due to the high speed requirements, I whipped up a small board with four MOSFET switches to instead drive the feedback signals - due to their 12V and 48V levels the Arduino can't directly drive them. A quick check on the breadboard verified the suitability, with the IRF520N transistors I had in the shop turning on and off in mere nanoseconds, approximately a million times faster than the relays could operate. 

The 1053 has two SMS paddle cards that plug into the signal SMS connector block of the 1130 and one SMS power paddle card that plugs into the power SMS block. These are swapped with the cards from my simulator to make use of the simulator instead of the physical typewriter. 

I am loaning the 1053 simulator for an indefinite period to allow the System Source Museum to demonstrate their IBM 1130 even when the console printer, the most trouble-prone part of the system, is inoperative. This also saves on paper use since the paper forms needed for the 1053 have to be custom manufactured and thus are expensive. 

Diagnosed failure point of Calcomp 565 plotter carriage stepper circuit

SINGLE POINT OF FAILURE MUST BE SHORTED TRANSISTOR

The symptoms were that the ring counter was not advancing in either direction. That implied a single failed component must cause this since different parts were involved in moving based on the direction. 

The ring counter has three stages, each driving one coil of a stepper motor. The design is such that only one of the three stages has its output conducting at any time. A request to shift the ring counter comes in through two paths, one to shift to the right and the other to shift to the left. 

If we imagine that the ring counter is currently operating with the first stage active, then a shift right pulse will be passed only to the trigger transistor of the second stage. A shift left pulse is passed only to the trigger transistor of the stage 3. 

The one stage that is conducting permits the shift pulse to be passed to the next stage. When a pulse turns on the next stage, the voltage at the conducting transistor forces the other two stages to turn off. 

I verified that the output transistor for stage 1 was conducting and that it was passing the shift right pulse to the trigger transistor of stage 2. However, stage 2 did not switch on, there was only a very short blip. Further, since it did not switch on, stage 1 was not forced to turn off. That might look as if it could be caused by a bad trigger transistor for stage 2, except that the same failure occurs with a shift left pulse which involves a completely different stage and trigger transistor. 

If, however, the germanium PNP output transistor of stage 1, a 2n392, had failed in a short circuit then it would effectively be conducting at all times. Initially it would direct the shift pulses to stage 2 or stage 3 trigger transistors, but would continue to conduct which would immediately force those other stages back off. 

REMOVED THE SUSPECT TRANSISTOR - STEPPER NOW MOVING PARTIALLY

I pulled the transistor off the board. That would allow the trigger to move the ring counter to stage 2 or stage 3 depending on whether we selected Carriage Right or Carriage Left, but it would not be able to move back to stage 1. It was enough to verify that a permanently conducting (effectively shorted) transistor was causing the symptoms.

TRIED TO MOVE SAME TRANSISTOR TYPE FROM PEN UP/DOWN CIRCUIT - ALSO BAD

The flip flop circuit that drives the pen solenoid is triggered by Pen Up and Pen Down commands, which should alternate turning the solenoid on and off. I get good trigger signals when the switch is moved but their is no change in the output transistor.

Since it was the same type of transistor (2N392), I pulled it to see if it was good and might temporarily give me a working carriage stepper. Alas, it too was stuck on, both in the pen solenoid circuit and therefore for stage 1 of the carriage ring counter when I moved the transistor there. Ordered another 2N392 from eBay. 

Adjusting System Source Museum 1053 console printer (typewriter)

ADJUSTING THE MACHINE TO CORRECTLY SELECT CHARACTERS FOR PRINTING

There are two aspects to adjusting the Selectric mechanism correctly for printing characters - tension on the two metal tapes and timing. The metal tape bands pull on components inside the carrier to twist the typeball to a specific column and to tilt the ball up or down to a specific row. The ball is locked into position at a defined time as it is pivoted forward to strike the ribbon, which must be related to when the tape tension is changed and when it must hold steady. 

A print cycle is the process that begins by moving the selection levers and ends when the typeball returns back to rest position after having struck a character on the paper. The selection levers are pulled down at the early part of the print cycle, which apply differing amounts of tilt to the levers that the metal tape bands run around. Tilting the lever further from the side of the frame will add tension to to the tape band that runs over the pulley, while tilting it inward will release tension. 

Thus, the lever and pulley that the rotate tape runs over will move up to five steps outward and five steps inward to select among eleven levels of tension on the rotate metal tape. The coil spring under the typeball resists the rotate tape tension, so that relieving a bit of tension will allow the spring to turn the ball one way, while adding tension turns the ball the other direction. 

The lever and pulley that the tilt tape runs over can move up to three steps outward from the frame, selecting among four levels of tension. A spring resists the tension of the tilt metal tape, but when the tension increases the cam that the spring pulls on will turn stretching the spring. This is transmitted to a gear that tilts the typeball to its row (tilt) positions. 

It takes a bit of time in the print cycle for the selection levers to be fully set and thus the tension on the two metal tape bands is changing during that time. Once the levers have settled to their full positions, the tape tensions should be static. At this point, a detent lever is lowered into the notches on the bottom of the typeball. This forces the ball to a more exact alignment of the column of type above and holds the ball steady while it is striking the ribbon to produce a character. 

The lever must NOT detent until the two tapes have stopped moving, otherwise the change in tension of the tape no longer produces movement of the ball, instead putting stress on the metal. They can fatigue and eventually break if the tape tension changes when the ball cannot move. Similarly, if the typeball is twisted by hand when the tapes are not changing tension, it can put stress on the tape and lead to fatigue failure. 

As well, after the ball has struck the ribbon but before it returns to rest position, the selection levers begin to restore to their idle position and the two metal bands change tension back to their rest states. The detent lever MUST be removed from the typeball before the tape tension changes, otherwise we again can strain the tapes leading to failure. 

The adjustments for timing must ensure that the detent lever is in the notches of the typeball only when the tape tension is not changing. It must enter before the ball hits the ribbon and it must disengage before the selection levers begin restoring. 

 

The adjustments for selecting the correct character must ensure that when the selection levers pick among the 11 column and 4 row positions, the ball turns to the intended row and column. Detents in the typeball notch (and underneath on the tilt mechanism) will adjust for minor misalignments and hold the ball steady during that midpoint of the print cycle. 

Ideally the ball is perfectly aligned for all of the tilt and rotate targets, but real world variations exist in the parts. Thus, the detent levers make fine adjustments - the more they have to adjust, the more strain on the tapes so we want to be as close as we can to perfect. 

One addition factor complicates things. The shift mechanism selects from one of two hemispheres of the typeball. On a typewriter, these are upper and lower case characters, but on the typeball with the IBM 1130 there are only upper case letters. Instead, it is numerals and special characters that exist only one one side or the other. 

The shift mechanism has its own lever and pulley on the right frame of the typewriter. It can pull the rotate metal tape band to add enough tension to spin the typeball 180 degrees. This is in addition to the tension adjustments performed by the rotate lever on the left frame. Ideally this is exactly 180 degrees but in the real world it is not. Thus, we have to check for the alignment of the typeball for the eleven rotate columns on both sides of the typeball. 

A given column might be exactly right on the 'lower case' side but off a bit on the 'upper case' side, due to variations. We want to find the best adjustments of everything to minimize the error in positioning for all 88 characters, two hemispheres by four rows by eleven columns of shift, tile and rotate. 

These adjustments are interrelated and take quite a bit of time to dial in to a suitable accuracy. This involves hand cycling the print cycle, adjusting gear positions to time the detent lever movements, and changing lever points and rod lengths until the row and column positioning of the typeball JUST BEFORE detent engagement are as spot on as possible. 

LOOPING THROUGH ADJUSTMENTS - EACH ONE AFFECTS THE OTHERS!

The adjustment instructions give a sequence of parts to check and adjust, as if it were a linear process that results in a perfectly working machine when you finish the last step. If only that were true, I would have been done several hours ago.

Instead, each adjustment may shift the parts involved in prior adjustments, so that they are no longer set to the desired position. One needs to iterate through the adjustments, hopefully so that the deviations shrink over time and the results are 'good enough' when you hit the last step once again. 

Replaced rotate and tilt tapes on System Source Museum 1053 console

CONSOLE PRINTER FROM SSM'S 1130 BROKE ITS TAPES

I received the console printer (1053, a Selectric mechanism driven by the computer) as the rotate and tilt tapes had broken when it was being used at their museum. I have new tapes which I am installing before adjusting the typewriter for proper typing behavior. 

INSTALLING THE ROTATE TAPE

This metal band will cause the typeball to spin, selecting which hemisphere (upper or lower case side) as well as which of the eleven columns on a side is to be printed. It is anchored to the moving carrier on the right side, runs through the frame on the right around a pulley on a lever arm, then passes underneath the carrier to the left side of the frame where it again passes over a pulley before it enters the carrier on the left side. 

We begin by inserting an eyehook on one side of the tape into the right of the carrier where a vertical screw holds it in place. The tape is threaded back and forth until it is ready to be inserted in the left side of the carrier. 

The rotate tape is wound around a drum which has spring tension keeping the metal band taut. As the pulley on the left side moves it selects one of the eleven columns, and the lever on the right chooses one hemisphere or the other. 

The typeball is rotated by hand four turns plus a bit to wind up the spring of the drum. The other end of the rotate tape has a T shaped end which is placed into a slot on the drum. The drum is then allowed to turn, releasing spring tension and pulling on the rotate tape until all slack is removed from the tape. 

Sounds easy? It isn't. You need one hand carefully maintaining tension at all times on the tape, a second hand to hold the typeball and turn it gently, and a third hand to release and reactivate the detent. The tape tries very hard to jump off the drum it is winding on, instead wrapping around the axle. 

INSTALLING THE TILT TAPE

The tilt tape also has an eyehook end which is attached to the same screw that holds the rotate tape on the right side of the carrier. It is all too easy to have the rotate tape eyehook slip off while you are trying to add the tilt tape eyehook. The tape is then routed over a pulley on the right side of the frame, back under the carrier to the left side of the frame where it goes over a pulley on a lever that can move to select one of four rows of type around the typeball from top to bottom. 

The other end of the tilt tape has an eyehook which passes into the left side of the carrier and is placed into a plastic rotary piece that is linked to the tilt gear of the typeball. That rotary piece is pulled by a spring, with the tilt tape pulled taut. As the lever on the left side moves outward, it pulls the rotary piece around against the spring tension to tilt the typeball to the chosen row of characters. 

This tape is less challenging to install, but does still need three hands or more at certain points in the process. Threading it below the carrier was the hardest part but eventually I had to routed over the tilt actuating lever and back into the carrier for attachment to the pully for the tilt gear. 

Debugging failure of carriage to move on Calcomp 565 plotter

SYMPTOMS OBSERVED

Operation of the manual carriage control to move the motor left or right had no effect. The same was true when the controller card in the 1130 sent a pulse to shift the carriage right or left. The first coil of the motor was always energized, the other two were not, and thus the motor held its position. The fast step manual switch for right or left carriage also did nothing. 

OVERVIEW OF CIRCUIT

The stepper motor that moves the carriage left or right has three coils, one of which is always energized and the other two off. By changing which of the three is energized, the motor moves one step in the direction of the new energized coil. The three coils are drive by a ring counter that moves between three states in both directions, based on a pulse to shift either to the right or two the left. 

One-shots generate a pulse and debounce the triggers to shift the ring counter left or right. The one-shot can be triggered by the manual control switches on the plotter or by a pulse on the interface from the computer to the plotter. 

The connection of the one-shots for right and left to the ring counter right and left shift inputs is routed through limit switches on the ends of the carriage. If the switch is depressed by the presence of the carrier at that extreme, any pulse to move further in that direction is blocked from the ring counter. 

CHECKING LIMIT SWITCHES

The contacts in the limit switch must be conducting in order for the pulses to get to the ring counter and shift it. I checked the conductivity of the switch using an ohmmeter. The contacts might have tarnished with age, growing a non-conducting layer. This can be fixed with contact cleaner and a burnishing tool. Fortunately, these were in good condition with very low resistance. 

CHECKING ONE SHOT OUTPUTS

The two one-shots, left and right, can be triggered by the manual control for that direction or by the interface input for that direction. The one-shot is a cross coupled set of transistors with an RC constant that holds the second transistor on for a fixed interval then returns the pair to the stable state where only the left transistor is conducting. 

I checked the voltages on the two transistors to verify first that they were set in the stable state with the left one on. I then used the manual control, watching the pulse and the right transistor to see that it turned on, cutting off the left. Finally, I watched the state revert to the left transistor on after the RC interval of about 1500 microseconds. 

The one-shots were producing perfect 1500 us pulses, however the ring counter wasn't moving. There are separate circuits for carriage left and carriage right movements, feeding a shift left and a shift right signal to the ring counter. Both sides worked, both for the manual movement switches and for computer interface commands.

CHECKING RING COUNTER OPERATION

The ring counter was initially sitting with the first stage active, energizing current through coil 1 of the stepper motor. Triggering a shift right pulse from the right one-shot, I watched to see if the transistors in the middle stage activated from the pulse. The middle coil should now be energized, with the other two stages cut off. Similarly, with the ring counter sitting with the first stage active, a left shift pulse from the left one-shot should activate the transistors in the third stage and energize that coil, cutting off the first and second stages. 

The counter never moved, with either type of shift request. On the correctly working drum movement side, the circuit feeding the second coil would snap on crisply and cut off the original coil. On the carriage ring counter, I saw a very short pulse as an attempt to turn on the transistor but nothing changed. 

The circuit uses older germanium transistors; the transistor that did not turn on is a 2N1304 type. To all appearances the transistor is bad, since the diodes and voltage levels around the circuit all seem to be good. However, I am suspicious since the counter does not shift in either direction. It we had a failed transistor for coil 2, that would fail to shift in one direction but going in the other should successfully activate coil 3. 

I will have to study the schematic and look for all the possible single points of failure that would block this from advancing in both directions. If it is one of the germanium transistors, I should be able to find them or a close substitute at worst case. 

ADDITIONAL MISSING PART IDENTIFIED

I began to string the the cables that pull the carriage left and right across the width of the drum, when I realized that I am missing the spring that provides the tension for the cables. There are two, attached the each side of the carriage and then routed through pulleys to the mechanisms inside the case. 

The cables also carry the 24V power to activate the pen solenoid on top of the carriage. Portions of the cable are in a plastic sleeve, providing insulation, with the back portions left as plain wire. The two pulleys on the rear are thus insulated from the machine chassis, used to connect the solenoid voltage to each cable. The two cables not only meet at the carriage, they also meet at the rear of the plotter where they are hooked to a spring (using insulated eyelets on the end). 

Those two eyelets are connected to the ends of a spring, which pulls the cables taut and maintains tension while the pair move the carriage. A round hub on a stepper motor is what moves one of the cables, the spring and other side the carriage moving the other cable in concert. 

Friends at a museum with an 1130 are going to measure the spring, both size and its reaction to a pull. With that information I can find a suitable replacement that will fit into the rear of the plotter and provide the intended tension. 

Restoring a Calcomp 565 plotter for use with my IBM 1130 system

SOMEONE DONATED THIS PLOTTER TO ME - IT WAS IN SAD SHAPE

The plotter had been damaged when something in a moving truck fell down and dented the drum of the plotter fairly severely. In addition, the prior owner had disassembled it for unknown reasons and it was given to me as a pile of parts and a partially disassembled jumble. It was also missing the solenoid that holds the pens. 

FRIEND OFFERED TO STRAIGHTEN THE DRUM BUT RESULTS WERE NOT GREAT

I got the drum back with the dent hammered out but the drum was out of round, with dips and bulges since the aluminum had stretched during the dent repair. It is not good enough to draw graphs on. It sat in the shop for a long time waiting for some inspiration on how to repair it.

Some years ago, a reader of my blog offered to 3D print a drum but that trailed off to nowhere. Again, I waited for inspiration. I have not yet developed a high confidence plan for a replacement.

Part of the issue is that the left and right sides of the drum have pins that mate with pin feed paper, so that the drum will pull the paper up or down as it rotates. Even if I found a source to make or buy a hollow aluminum drum of the right dimensions, I would have to recreate the pins. 

MADE USE OF THE PLOTTER TO TEST MY CONTROLLER CARD FOR THE 1130

As part of the successful project to build a card and connectors to upgrade an 1130 to add support for an IBM 1627, which is a relabeled Calcomp 565 or 563 sold by IBM, I partially restored the plotter to verify that a plotter would be controlled by my card. 

It took several hours to carefully assemble the parts sufficient to attempt the testing. I had first tested the power supply and found it working properly. I then used the manual controls on the plotter to test out movement of the drum (up and down), the carriage (left or right) and the solenoid to lower the pen onto the paper. 

SOME PARTS OF THE PLOTTER ARE NOT WORKING CORRECTLY

3I discovered that the carriage movement circuitry is not working properly. Neither the manual controls nor pulses from a bench test setup nor from the 1130 controller card would cause the stepper motor to move. The power transistors for the stepper motor remained holding just one coil active, ignoring any attempt to change the ring counter to select an adjacent coil. This will need to be debugged. 

The chart paper motors, which keep tension on the rolls of chart paper that is moving through the drum, did not move. They are both physically frozen in place - I suspect congealed lubricants are the cause.

I have to restring the cables for the carriage movement, although I also need the stepper motor working for this to matter. With that in place and once the stepper is working, I can check for solenoid power with the pen raise and pen lower commands. I am assuming this circuitry works properly but it has not been tested.

MISSING SOME PARTS

I was missing the 5/16-32 panel nut that holds the power on/off switch onto the panel. It is hard to find that size nut, as the retailing world seems to be concentrating on 3/8" and metric nuts. There are also quite a few screws missing from the pile I received, a mix of 4-40 and 6-32 sizes. I will fill in all the missing locations when I replenish my screw stock. 

BUILDING A PEN SOLENOID REPLACEMENT

The plotter has a pen holder with a solenoid inside that is attached to the top of the carriage. It will lower a pen onto the paper or lift it off. The holder from Calcomp had several attachments for different types of pen inserts. 

I came across a Calcomp holder and solenoid that was used for a cutter instead of a pen. It sat on the same plotter mechanism but was used to cut plastic, paper or fabric. Since its shape and functionality is identical to the pen version, other than having a cutter instead of a pen insert, it should be easy for me to work out a way to put a pen in the holder. 

NEXT UP - LOOK INTO THE ISSUE WITH THE CARRIAGE STEPPER MOTOR

When I have time in the workshop, in between higher priority projects or tasks, I will dive into the logic and figure out why the carriage is not moving with manual or interface commands. At the same time I will do a quick check to see if the flipflop for pen lower/raise is working and if the circuit is driving voltage when the solenoid should be activating. 

Testing with a Calcomp 535 - part 2

MEASURING -34 VOLTS IS OKAY WHEN THE SUPPLY IS UNCONNECTED

Two factors contribute to a higher unloaded voltage observed on the -24V rail. First, the nominal AC mains voltage was bumped up from 115V to 120V at some point after the plotter was designed. Second, voltage drop takes place in the transformer secondary windings when it is under load that reduces the output voltage compared to the very high impedance of an unloaded measurement. 

MOVING FORWARD TO TESTING

I tested the logic boards to be sure that there were no short circuits that might damage the power supply rails. After this point, I felt comfortable that the worst I would be facing is incorrect behavior, not dramatic failure. I hooked up the logic board to the power supply, controls and stepper motors, again checking for unexpected short circuits. 

There are two ring counters in the plotter - one for the pen carriage moving left or right, the other for the drum to roll up or down. These drive current through one of three pairs of coils in a stepper motor, with the active coil pair moving each time we shift the ring counter. 

The final circuit is a flipflop for pen up versus pen down on the paper. A falling edge on one side sets the flipflop to 'pen down', a falling edge on the other changes the flipflop to 'pen up'. This either energizes the solenoid in the pen or turns it off to allow the pen to move back under spring tension. 

My first tests used the manual controls on the plotter. This verifies that the motors move one step in each direction and that the ring counters are functional. It is a fairly good test of the plotter circuitry. The circuit for the drum movements worked perfectly, single stepping and then moving 120 steps per second with the fast mode manual control. The carriage left or right controls did nothing - no single step, no fast movement. 

There is something wrong with the plotter concerning the carriage movements. I don't have the plotter assembled enough to power the solenoid since its power travels through the cables which pull the carriage left or right and those are not connected yet. Thus all I can test with the plotter in its current condition is whether the controller card can move the drum up or down one step in response to an XIO Write. 

TESTING THE INPUTS FROM THE 1130

Then I used my bench testing setup to try to make the steppers work with triggers from my breadboard device. The circuitry looks for a falling edge on the control inputs to advance a ring counter in one direction or another - the outputs of the ring counter are fed to the poles of the stepper motor, so that one step of the ring counter causes one increment of rotation on the motor.  

The bench setup uses pullup resistors to 12V and a pushbutton to drop each of two lines to ground when I activate the button. My scope could show me the state of the ring counter which would let me verify that it moves one step in each direction on command.  Alternately a voltmeter on the collector of the driver transistor for each of the three coils will show two at -24V and one at ground, shifting which is grounded as the ring counter advances. 

Indeed, the button press resulted in a one step movement in the direction I requested, exactly the same as the manual control on the plotter. Since this mirrors how my controller card drives the plotter, I fully expected the final testing on the 1130 to succeed too. It was time to connect to the 1130 and try it out. 

TESTING WITH THE IBM 1130 SYSTEM

I hand toggled some commands into the 1130 system so that I could execute XIO Write and XIO Sense Device commands. The goal was to mirror the tests from the bench. 

I coded an XIO Write with the data word set to request an up movement, followed by an XIO Sense Device and then a wait instruction. I should see the status with bits 14 and 15 set in the accumulator register (ACC). The 1130 should have taken a step into the interrupt handler for level 3, which I set up with a wait instruction. The stepper motor should have moved one step. 

I then have an XIO Sense Device followed by another wait instruction. This is in the interrupt handler code. I should see bits 0 and 15 in the accumulator, since the movement is complete. The next instruction is an XIO Sense Device with Reset bit 15 followed by a branch out of the interrupt handler. I should return to a wait instruction following the original XIO Write and Sense Device code. 

I can update the data word and do the above a second time, so that it is now requesting to turn the drum down. This too worked properly. I set up a loop so that my program issued drum movement commands as fast as the prior one completed and we returned from the interrupt handler. The drum moved rapidly, even faster than the manual fast mode control. 

Ultimately, I powered off the Calcomp to test its behavior in that mode. When I issue the XIO Sense Device I should see that no bits are on. Doing an XIO Write to request an up movement should turn on the interrupt request but an XIO Sense Device will show only bit 0 turned on indicating that the movement completed but the plotter is not ready. 

That is exactly how it behaved. Everything I could test was working exactly as it should.