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PS-2/RS232 to ASCII Keyboard
Adapter Assembly and Operations
By Mike Willegal
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.
•
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.
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.
Guide
www.willegal.net
CAUTION!!!
Changes Made for Version 2.2
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version 2.2
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Summary of Contents for Mike Willegal PS-2/RS232 ASCII Keyboard
- Page 1 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.
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Page 2: Recommended Tools And Equipment
Chapter 1 – Assemble Components, Tools, and Equipment Recommended Tools and Equipment • Quality soldering station - I use a Weller WES51. Whatever you use, I recommend that it has some kind of temperature controlled tip. This will help prevent damage to the PCB when soldering •... - Page 3 Compare Received Components With Parts List Examine and identify all parts provided with the kit. PART DESCRIPTION QUANTITY PRESENT MAX202CPE RS232 Transceiver 16 pin DIP package (not socketed) .1uF capacitors Used with RS232 transceiver 47uF capacitor Power supply smoothing DB9 male connector RS232 connector din6 PS/2 keyboard connector...
- Page 4 Chapter 2 – Solder In Components Overview The key thing here is to check orientation and make sure that you don’t put the sockets or MAX202 chip in wrong. Make sure that the parts are oriented correctly with pin of the socket or chip near the bottom of the PCB.
- Page 5 PART DESCRIPTION QUANTITY COMPLETE Pin 1 has square pad on top side of board (pin 1 toward www.willegal.net). This chip is not socketed because I have never had one fail or reason to remove one from MAX202CPE it’s socket. If you have an extra 16 pin socket, and prefer having socketed parts on your adapter, putting a socket here will not have adverse affects on operation.
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Page 6: Electrolytic Capacitor
Electrolytic Capacitor Orientation is critical. Double check this work. Incorrect insertion can result in fire! PART DESCRIPTION QUANTITY COMPLETE Orient * and - leads to match + and - signs on silk Failure to do so may result in damage to the 47uF capacitor screen. adapter and connected equipment and possibility of fire. page 6... - Page 7 Diode This diode is only required if using the adapter with an Apple . Chapter 3 has a description of the clear function that is associated with this diode. silk screen orientation The diode must be oriented correctly. There are two ends, anode and cathode. Be sure that orientation matches the silk screen.
- Page 8 Chapter 3 – Wiring Jumper Area This adapter has a flexible jumper area that is used to connect a 16 pin keyboard ribbon cable header to the mi- crocontroller that is the brains of the adapter. This jumper area contains 2 rows of pins. The connections can be made by direct jumper, wire wrap or through a removable header.
- Page 9 Adapter Interface Details The connection area consists of locations for 28 pins in 2 rows of each row. 6 of the pins connect directly to the 6 pin DIP header labeled “KEYBOARD”. These pins are labelled through 6 and connect directly to the same numbered pin on the 6 pins DIP header.
- Page 10 Apple II Example: The Apple II and II plus keyboard socket has the following pinout. Double check your connections with an ohm meter prior to powering up. Incorrect connections, especially to the -2 volt pin can damage your adapter or the host computer. Be sure to check for shorts between adjacent connections. Later Apple computers like the IIe use different technology for keyboard interfacing and are not compatible with this adapter.
- Page 11 Apple 1 Example: The Apple keyboard socket has the following pinout. Double check your connections with an ohm meter prior to powering up. Incorrect connections, especially to the +2 or -2 voltages can damage your adapter or the host computer. Be sure to check for shorts between adjacent connections. Add the SI shunt for automatic reset and clear after power up.
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Page 12: Rs232 Interface
Chapter 4 – The Cables and Plugging It In The Ribbon Cable The ribbon cable and connectors are not preasembled. This allows the adapter owner to assemble the cable into the best configuration for his application. Because of possible issues with power drop over the length of a longer cable, it is recommended that ribbon cable length be kept to foot or less, If a longer ribbon cable is needed, separate provisions may have to be made for supplying + volts and ground to the adapter. -
Page 13: Chapter 5 - Special Features
Chapter 5 - Special Features 1. PS/2 Keyboard KEY SEQUENCE DESCRIPTION Control-ALT-DEL Asserts reset Caps-lock Toggles between upper and lower case input Num-lock Num lock is always on - cursor controls on keypad can not be enabled If A2 shunt is in place, arrow keys will cause Apple 2, esc-x cursor control se- Arrow keys quences to be sent when arrow keys are pressed Control-R... -
Page 14: Chapter 7 - Troubleshooting And Help
Chapter 7 – Troubleshooting and Help A good job of soldering the components into place should eliminate most if not all trouble. First step, in case of trouble, should be to check for bad solder joints or bridges. Refer to my Apple II repair page at www.willegal.net for some general troubleshooting hints.
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