In 1979 I interfaced my MEK6800D1-based microcomputer to a Kleinschmidt AN/FGC-25 Teletypewriter set that I repaired and rebuilt in 1978. Over the past several months, off and on, I got the old teletype set back in operation after having been in basement storage for the past 20 years. The most significant problem I had was failure of two electrolytic capacitors in the selector magnet bias circuit for the printer. I posted a demonstration of the working printer here; http://www.zippcast.com/video/a722081e609549512fa
Below is a diagram of the computer interface that I made back in those days. The output transistor is a high voltage type for operating the 60mA current loop.
The M6800 uses the 1 millisecond timer for timing the mark/space signaling; 22 milliseconds for the start bit and five character bits, and 31 milliseconds for the minimum stop bit period.
This interface worked fine, but almost as soon as I got it working I abandoned my hobby activity when I went back to graduate school.
I recently developed a modified interface design that uses a diode bridge and an opto-isolator instead of the transistor, so that the computer and the teletype set are electrically separate. With the bridge, the current loop polarity does not matter. After I get the entire hookup going again, I plan to upgrade the interface with the bridge and opto-isolator.
I have completed the hardware design for an input interface for the current loop, also using an opto-isolator.
I plan to update this post as I make progress, just like DaveH and his 6809 Flex progress, which I am interested to read about.
-73
Below is a diagram of the computer interface that I made back in those days. The output transistor is a high voltage type for operating the 60mA current loop.
The M6800 uses the 1 millisecond timer for timing the mark/space signaling; 22 milliseconds for the start bit and five character bits, and 31 milliseconds for the minimum stop bit period.
This interface worked fine, but almost as soon as I got it working I abandoned my hobby activity when I went back to graduate school.
I recently developed a modified interface design that uses a diode bridge and an opto-isolator instead of the transistor, so that the computer and the teletype set are electrically separate. With the bridge, the current loop polarity does not matter. After I get the entire hookup going again, I plan to upgrade the interface with the bridge and opto-isolator.
I have completed the hardware design for an input interface for the current loop, also using an opto-isolator.
I plan to update this post as I make progress, just like DaveH and his 6809 Flex progress, which I am interested to read about.
-73