Apple 1 Serial Board Enables 9600 baud display and data entry

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Apple 1 Serial Board Enables 9600 baud display and data entry

This Apple 1 Serial card  uses the  VMA line to replace the on board Keyboard and Display with an RS232 Connection.The VMA line is normally shorted to +5V but can be used by replacing the short with a Resistor and Capacitor.  The capacitor is needed due to noise problems on the board.  The RC can replace the short to +5 on the Apple 1 board with little visual impact using 0402 or 0201 surface mount R and C (see Photo)  or can be connected between pins 12 and 14 of B1 with standard parts.  When the VMA line is pulled down all I/O, RAM and ROM are disconnected and can be replaced by other circuits.  The Serial Card looks at the Address lines and will pull down the VMA on cycles with address $D010 to $D012 when the KBD or Display functions are enabled to disable the on board I/O and replace it with equivalent information from the Serial Card.  If the Serial port is connected by RS232  to a Computer, a Terminal window can replace the Apple 1 screen and the computer keyboard becomes the Apple 1 keyboard.  Now the display and keyboard rate can approach the Baud Rate of the Serial connection.  A video of 9600 baud operation is at:

https://youtu.be/FIVN6NgGdK4

The FRAM board uses the same VMA line to change DRAM and monitor ROM addresses from the Apple 1 board to the FRAM board on a cycle by cycle basis.  A demo is at:

https://youtu.be/mPXJ1EYHrhw

 

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Last seen: 4 days 9 hours ago
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Serial Card Photo
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Last seen: 4 days 9 hours ago
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Apple 30th Aniversary at 9600 baud
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