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MicroCoreLabs 2019-11-09 21:17:04 -08:00
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MicroCore Labs - Arduino Leonards-based IBM Wheelwriter Printer Option
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Description:
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This is an Arduino Software project which allows RS232 access to an IBM Wheelwriter Typewriter.
Using a terminal running at 300 baud (300,n,8,1), the user can directly send characters to the typewriter.
They can also cut and paste long documents into the terminal, which will be printed by the typewriter.
It has been tested on an IBM Wheelwriter 5, however other IBM typewriters such as the Wheelwriter 3 and 6 may also work.
The only connection needed to the typewriter is via two pins within the access panel at the top rear of the typewriter.
I am using an Arduino Leonardo board which uses the ATmega32u4 microcontroller which contains two UART controllers.
This design uses both UARTS. One is connected to the host at 300,N,8,1 and the second connects to the IBM Wheelwriter's IBM_BUS
interface which runs at 188k, N,9,1. The UART is used in a non-standard 9 databits operation which is not directly supported
by the Arduino software base. I needed to directly write a few registers to active this mode.
The IBM_BUS is bi-directional, so the Arduino's UART Transmitter must be deactivated and set to hi-Z so it will not conflict
with the drivers contained in the typewriter. To save time I simply added a delay to give the typewriter time to ACK on the IBM_BUS
rather than sample it for the ACK response. Faster printing action could be achieved if a separate bus transceiver was used
to switch on and off between the Arduino and the typewriter driving the bus.
There is very limited buffering in the Arduino's UART transmitter and reciever and I have also provided very shallow buffering,
so characters must be sent from the host at the pace typical of typing on the typewriter by hand.
Pinout
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- The IBM Wheelwriter pins of interest are: 4=GND and 5=IBM_BUS. Pin#1 is on the left when looking at the typewriter from the front.