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PS-2/RS232 to ASCII Keyboard
Adapter Assembly and Operations
Guide
By Mike Willegal www.willegal.net version 2.2
CAUTION!!!
Incorrect assembly and interconnecting of this adapter can cause fatal damage to the interface and/or the host
computer. Double and triple check your connections before powering on. Pay special attention to the +2 and
-2 voltages that are present on many of host computer keyboard sockets. These voltages are not required for
operation of this interface and should not be connected. Plugging in the connector backwards when connecting
to an Apple will invariably destroy the micro-controller on this adapter and may cause damage to the com-
puter.
Changes Made for Version 2.2
The data invert functionality has been dropped . If you need inverted data, you can use external invert-
ers to accomplish the same functionality.
The jumper that used to control inverted data, is now used to control automatic reset and clear. Auto-
matic reset system and clear screen upon power up is now disabled, unless the jumper is inserted.
A behavior that sometimes caused multiple resets when control-alt-delete reset sequence was used has
been eliminated. Once reset occurs, all three keys must be released, before control-alt-delete can cause a second
reset. The control-r, control-s, control-t reset functionality is unchanged.
Forward
A number of vintage computers of the 70’s and early 80’s were designed to support a keyboard with a simple
parallel ASCII interface. These keyboards can sometimes be hard to find, the most common source being com
-
plete Apple II plus computers. This adapter allows you to connect a slightly more modern PS/2 style keyboard
with a 6 pin mini-DIN connector to a vintage computer expecting a parallel ASCII interface. In addition, it
provides a RS232 input capability to the same vintage computer. This adapter will not work with Apple IIe or
later model Apple computers. Though I haven’t tested it, I expect that the adapter will work with other makes
of vintage computers that expect keyboard input with a similar parallel ASCII interface. Specifications of the
interface are provided in this guide.
In addition, this adapter supports several special functions for Apple and Apple II/II plus computers.
Assembly and testing of these adapters can be done for the user for an additional fee. The purchaser must spec-
ify whether the assembled and tested interfaces should be configured for Apple 1 or Apple II/II plus computers.
I am unable to build adapters for other computers, because I can not test them.
The power draw of this adapter when connected to a PS/2 keyboard and RS232 interface is nearly beyond the
limits of a DIP socket and single AWG28 power supply wire in the ribbon cable. Do not use a ribbon cable lon-
ger than necessary. If you are experiencing intermittent operation, try connecting a separate power and ground
wire pair between the adapter and the computer.
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