I'd assume that process is designed for mechanical typewriters, which would relatively easy to convert to a computer interface because of their simplicity. As for the Selectric, Wikipedia has this rather ominous blurb of text -
Quote
Despite appearances, these machines were not simply Selectric typewriters with an RS-232 connector added. A Selectric is a marvel of mechanical and production—but not electronic—engineering. As with other electric typewriters, and electric adding machines of the era, Selectrics are best thought of as electromechanical devices: The only electric components are the power cord, power switch, and electric motor. The electric motor runs continuously. The keys are not electrical pushbuttons, as they are on a computer keyboard. Pressing a key does not produce an electrical signal, but rather engages a series of clutches which couple the motor power to the mechanism to turn and tilt the element. A Selectric would work equally well if hand-cranked at sufficient speed.
Adapting this mechanism to the needs of computer input/output was nontrivial. The keyboard and printing mechanism were mechanically separated (so that keystrokes do not necessarily result in immediate printing), microswitches were added to the keyboard, solenoids were added to allow the computer to trigger the typing mechanism, and interface electronics were needed. Several mechanical components, in particular the motor and the main clutch, had to be upgraded from the typewriter versions to reliably support continuous operation. Additional microswitches had to be added to sense the state of various parts of the mechanism, such as case (upper vs. lower).
Even after adding all those solenoids and switches, getting a Selectric to talk to a computer was a large project. The Selectric mechanism, as documented in its service manual, had many peculiar requirements. If commanded to shift to upper case when it was already in upper-case, the mechanism locked up and never signaled "done". Same thing for shifting the ribbon direction or initiating a carriage-return. These commands could only be issued at particular times, with the Selectric in a particular state, and then not again until the terminal signaled the operation was complete.
In addition the Selectric spoke neither ASCII nor EBCDIC, but a unique code based on the tilt/rotate commands to the golf ball. That and the bit-parallel interface and peculiar timing requirements meant the Selectric could not be directly hooked up to a modem. Indeed it needed a relatively large amount of logic to reconcile the two devices.
Logged