Mike Willegal PS-2/RS232 ASCII Keyboard Installation instructions
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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 +12 and
-12 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 1 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 nd, 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. Specications of the
interface are provided in this guide.
In addition, this adapter supports several special functions for Apple 1 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 congured 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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Chapter 1 – Assemble Components, Tools, and Equipment
1. 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
Solder - use quality solder - thinner solder is vastly easier to work with than fat solder. The fat
stuff sold at hardware stores is not suitable for these sort of electronics projects
Wire cutters – for trimming component leads and cutting wire to length
Wire strippers - for stripping ends of jumper wire
Sharp scissors - for trimming ribbon cable
Drill press, screw or vice clamp - for assembling plugs to ribbon cable
Your favorite PCB cleaning agent - Isopropyl Alcohol will dissolve many kinds of soldering
resin. Windex will also help with cleaning PCBs
Ohm meter - to check for good connections and shorts
Logic probe or oscilloscope – handy if you are having trouble with bring up
Your host computer schematics or hardware interfacing guide – Direction for connecting to
Apple 1 or Apple II/II plus computers are provided in this manual
2. Additional Components (not included)
PS/2 keyboard - The type with the smaller mini-DIN 6 connector is required
RS232 null modem cable - Conguration may vary depending upon specic PC you are
connecting your adapter to. Often a DB-9 female to DB-9 female NULL modem cable will
work. Pins 2 and 3 are crossed and pins 5 (ground) is connected straight through. Digikey part
number AE9879-ND is an example of such a cable.
PC with terminal software and serial port. Many modern PCs must be connected to RS232 serial
interfaces using USB to RS232 converters. Most of these types of converters will work with the
DB9-F to DB9-F null modem cable described above
3. EasyRecongurationOption(notincluded)
WARNING - only try this approach if you have the proper crimper tool
Header - Digikey part number 609-2434-ND
One or more shrouds - Digikey part number 609-2391-ND
Pins - Digikey part number 609-3614-1-ND
Wire - 22-26 AWG stranded wire
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4. 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) 1
.1uF capacitors Used with RS232 transceiver 5
47uF capacitor Power supply smoothing 1
DB9 male connector RS232 connector 1
din6 PS/2 keyboard connector 1
16 pin socket for keyboard to host ribbon cable connection 1
20 pin socket for AVR microcontroller 1
Attiny2313 preprogrammed and calibrated microcontroller 20 pin DIP
package 1
1’ ribbon cable keyboard to motherboard connection (cut to length) 1
ribbon cable headers connect to ribbon cable ends after cutting ribbon cable
to length 2
PCB printed circuit board 1
1N914 diode for Apple 1 clear function 1
2 pin KK style headers conguration headers 6 pin header provided (you break
apart into 3, 2 pin headers) 3
shunts conguration jumpers 3
3’ jumper wire for jumpering from microcontroller to keyboard header 1
PARTS COUNT 24
COUNT OF TYPES 15
page 4
Chapter 2 – Solder In Components
1. 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 1 of the socket or chip near the bottom of the
PCB.
Make sure the socket or chip is fully seated. I accomplish this by resting the socket upside down on a small
object with the board on top. The weight of the board should keep the socket or chip completely seated. Then
tack down a couple of corner pins and recheck orientation and seating. Then nish soldering the rest of the
pins.
Take your time and enjoy the process, double checking orientation of devices as you go. The blue arrows indi-
cate places to pay attention to orientation when placing components.
2. Check for Power and Ground Shorts on PCB
Easiest way to do this is to use an ohm-meter to make sure that there is no connection between power and
ground. A convenient place to use, is the positive and negative pins of electrolytic capacitor location (blue ar-
rows above).
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PART DESCRIPTION QUANTITY COMPLETE
MAX202CPE
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
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.
1
.1uF capacitors Orientation not important 5
DB9 male connector RS232 connector facing edge of board 1
din6 PS/2 connector facing edge of board. Fill in big hole
with solder in order to make connector more stable 1
20 pin socket For AVR microcontroller - Pin 1 has square pad on top
side of board (pin 1 toward www.willegal.net) 1
16 pin socket
For keyboard to host ribbon cable connection - Pin 1
has square pad on top side of board (pin 1 toward www.
willegal.net)
1
2 pin KK style headers 2 pin conguration headers labelled A2, SI and CR 3
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3. Electrolytic Capacitor
Orientation is critical. Double check this work. Incorrect insertion can result in re!
PART DESCRIPTION QUANTITY COMPLETE
47uF capacitor
Orient * and - leads to match + and - signs on silk
screen. Failure to do so may result in damage to the
adapter and connected equipment and possibility of re.
5
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4. Diode
This diode is only required if using the adapter with an Apple 1. Chapter 3 has a description of the clear
function that is associated with this diode.
AK
silk
screen
orientation
The diode must be oriented correctly. There are two ends, anode and cathode. Be sure that orientation matches
the silk screen.
PART DESCRIPTION QUANTITY COMPLETE
1N914 diode for Apple 1 clear screen function - not needed for Ap-
ple 2 or other applications - orientation is important 1
page 8
Chapter 3 – Wiring Jumper Area
This adapter has a exible 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.
Wire is provided with the kit for direct jumpering.
When doing direct wire jumpering, cut wires to length to provide a neater appearance. Wires should be stripped
at one end and soldered to the adapter at that end before cutting to length, stripping and soldering the other end.
If you want make the connections via wire wrap or a removable header, you must provide the additional com-
ponents required.
If you have access to the correct crimper tool, you can make a removable header. Be sure that you use a keyed
shroud and header that will prevent you from plugging the header in wrong and causing damage to the adapter
or computer. Suggested shroud and header parts are listed in chapter 1. Trying this approach without using the
proper crimper tool is likely to end in fustration.
Wire wrapping involves adding a 28 pin 2 row KK style header to the board and using a wire wrap tool and wire
to make the connection.
In all cases the connections remain the same.
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1. Adapter Interface Details
The connection area consists of locations for 28 pins in 2 rows of 14 each row. 16 of the pins connect directly
to the 16 pin DIP header labeled “KEYBOARD”. These pins are labelled 1 through 16 and connect directly to
the same numbered pin on the 16 pins DIP header. 12 of the pins connect to the microcontroller and are de-
scribed in the table below.
D0-D6 Data bits 0 - 6
TTL ASCII data output from micro-controller. Least signicant bit is
D0, most signicant is D6. Data is high true. Most common microcom-
puters (including Apple) expect high true data from an ASCII keyboard.
If your computer requires low true data, add inverters on the data
lines between the PS/2 adapter and your computer.
5V +5 Volt Supply
Connect to +5 Volt pin on keyboard header. Provides power to micro-
controller, RS232 interface and keyboard. PS/2 spec says keyboards are
allowed to draw up to 300 milliamps of current. The micro controller
and RS232 driver can draw up to an additional 15 milliamps of power.
This can stretch the capability of a 28 AWG wire in a ribbon cable
and DIP socket. For reliable operation, keep the length of the rib-
bon cable reasonably short. If you suffer from intermittent operation,
try adding separate power and ground wires from the adapter to the host
computer.
GND Ground Connect to ground pin on keyboard header
SRB Strobe (output
from adapter)
TTL output from microcontroller. Generates 125 micro-second positive
going pulse .75 micro-seconds after data is presented to D0-D6. Any
host that accepts parallel keyboard data and responds to a positive or
negative edge triggered strobe should work with this adapter.
RST Low true reset
signal
TTL output from micro-controller. Reset is a asserted as a low going
pulse lasting approximately 1.25 milliseconds. The PS/2 adapter can be
congured to automatically assert reset after the adapter is powered
up and initialized. To enable this feature, the jumper labelled “SI”
at the edge of the board should have a shunt inserted. Reset will also
be asserted when a control-alt-del sequence is typed on a PS/2 keyboard
and optionally if a control-R, control-S, control-T sequence is detect-
ed on either the RS232 interface or keyboard. The optional control-R,
control-S, control-T sequence can be disabled by inserting the CR jump-
er shunt on the adapter.
CLR High true clear
screen signal
TTL output with diode “OR” function. The signal is a high going pulse
approximately 40 milliseconds long. This is specically added to allow
clearing the screen on Apple 1 computers. The diode can be replaced
with a jumper wire for other applications that may have need for a user
controlled high going TTL level pulse. The PS/2 adapter can be con-
gured to automatically assert clear after the adapter is powered up
and initialized. To enable this feature, the jumper labelled “SI” at
the edge of the board should have a shunt inserted. It will also be
asserted if a control-C, control-L, control-R sequence is detected on
either the RS232 interface or keyboard. This optional control-C, con-
trol-L, control-R sequence can be disabled by inserting the CR jumper
shunt on the adapter.
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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 -12 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. See the fol-
lowing page for the Apple 1 conguration, which is not compatible with the II/II plus. The following jumper
connections should be made for the Apple II/II plus computers. Install the A2 shunt to enable arrow mapping
capability. Other shunts should not be installed.
AII or AII Plus
DIP SOCKET PIN NUMBER
MICROPROCESSOR
CONNECTION COMPLETE CHECKED
1 5V
2 SRB
3 RST
4 no connection
5 D5
6 D4
7 D6
8 GND
9 no connection
10 D2
11 D3
12 D0
13 D1
14 no connection
15 no connection*
16 no connection
* - 12 volts is on this pin on the computer’s 16 pin keyboard socket - connecting this pin will most likely dam-
age the adapter and possibly the computer
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Apple 1 Example:
The Apple 1 keyboard socket has the following pinout. Double check your connections with an ohm meter
prior to powering up. Incorrect connections, especially to the +12 or -12 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. In original Apple 1’s, it was a manual process, so leave the SI jumper discon-
nected for authentic behavior. The following jumper connections should be made for the Apple 1.
A1
DIP SOCKET PIN NUMBER
MICROPROCESSOR
CONNECTION COMPLETE CHECKED
1 RST
2 D3
3 D2
4 D1
5 D0
6 D4
7 D5
8 D6
9 GND
10 no connection*
11 no connection**
12 CLR
13 no connection
14 SRB
15 5V***
16 5V
* +12 volts is on this pin on the computer’s 16 pin keyboard socket - connecting this pin will most likely dam-
age the adapter and possibly the computer
** - 12 volts is on this pin on the computer’s 16 pin keyboard socket - connecting this pin will most likely dam-
age the adapter and possibly the computer
*** this pin is a provision for an 8th input data bit, but is normally connected the +5 volts. There is only 1 hole
for +5 volts and two wires going to it. I recommend connecting pin 16 to 5 volts with a bare wire and soldering
pin 15 to the bare wire going between pin 16 and 5 volts.
2. Clean PCB of Rosin and By-products of Soldering
Once soldering is complete, clean the back of PCB of excess ux and rosin. 90% or higher isopropyl alcohol.
IPA will dissolve soldering resin. Spray it on the back of the board and lightly scrub with a very soft brush that
will not scratch the surface of the PCB. Soak up the IPA and contaminates with a clean soft cloth before it
evaporates in order to remove the by products of soldering. Let dry overnight. Position a fan to blow over the
board to make sure that all remaining moisture evaporates.
I have also discovered that “Windex” window cleaner can help remove the by-products from the soldering
job. Removing contaminates is important as many kinds of rosins are corrosive.
3. Check Board for Solder Bridges and Cold Solder Joints
While the board is drying, you should carefully check your work for bad solder joints and solder bridges.
4. Insert Microcontroller
Pin 1 is toward WWW.WILLEGAL.NET etched in copper layer.
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Chapter 4 – The Cables and Plugging It In
1. The Ribbon Cable
The ribbon cable and connectors are not preasembled. This allows the adapter owner to assemble the cable
into the best conguration 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 1 foot or less, If a longer ribbon cable is
needed, separate provisions may have to be made for supplying +5 volts and ground to the adapter.
Cut the ribbon cable to length with a sharp scissors. Before pressing the cable into place, it is recommended
that the connector is plugged into a spare socket. This will help protect the pins from damage. The best way to
press the cable into place, is to use a press. A drill press can easily be adapted for the job. If a drill press is not
available, a screw clamp would make the next best tool for the job. Make sure you work out the best orientation
of plugs before pressing into place and make sure that the marked pin 1 side of the cable is at pin 1 of the con-
nector at both ends. A sure way to damage your adapter is to plug it in backwards. Having the markings on the
cable and plugs match actual pin 1 will help prevent you from making mistakes.
2. RS232 Interface
This cable is not provided. The pinout of the RS232 DB-9 male connector is as follows. A suggestion for a
ready made cable that will work with some commonly available USB to RS232 adapters is listed in chapter 1.
PIN DESCRIPTION
2 RX data
3 TX data
4 Always asserted - can be used as DTR
5 Ground
The RS232 interface is congured to run at 9600 baud, 7 data bits, even parity, with one stop bit. Congure you
PC’s terminal software to this conguration. The baud rate is generated using the microcontrollers internal RC-
oscillator. This oscillator is congured to operated at nominal baud rate at room temperature. I have not expe-
rienced this, but it is possible that at extremely hot or cold temperatures, that the oscillator will drift. This drift
may cause the baud rate change to a speed that is beyond the capability of RS232 protocol to correctly transmit
and receive data. Returning the system to room temperature should resolve the issue. If you encounter this is-
sue, record the temperature at which you experienced the problem and let me know about it.
3. Plugging It In and Powering It Up
Power off your computer before plugging in the adapter. Make sure pin 1 of the ribbon cable is connected cor-
rectly to the computer and adapter. It is easy to accidentally offset DIP plugs, so make sure pin 1 of the plug is
in the pin 1 position of the socket. Connect the PS/2 keyboard and/or the RS232 interface to your adapter.
When you power up, you should see the LED indicators of you keyboard blink as it runs it’s power on self test.
If the adapter doesn’t immediately establish good communication with the keyboard, the adapter will reset the
keyboard and this self test will be repeated. After a blink or two, the num lock and caps lock lights should
remain on, with the other light off. With the SI jumper in place, the adapter will autmoatically reset your com-
puter, and in the case of an Apple 1, it will clear the screen. If the SI jumper is not in place, you may need to
manaully reset it(control-alt-delete) and in the case of an Apple 1, clear screen (control-C, control-L, control-R).
At this point, if all is well, you should be able enter data into your computer using the PS/2 keyboard or RS232
interface. Either the PS/2 or RS232 or both interfaces can be connected and used at any given time.
page 13
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
Arrow keys If A2 shunt is in place, arrow keys will cause Apple 2, esc-x cursor control se-
quences to be sent when arrow keys are pressed
Control-R
Control-S
Control-T
If CR shunt is not in place, pressing these keys, sequentially, will cause reset to
be asserted
Control-C
Control-L
Control-R
If CR shunt is not in place, pressing these keys sequentially will cause clear to
be asserted. This is intended to clear the screen of an Apple 1 computer
2. RS232 Interface
The RS232 interface is a write only interface. Characters output by the vintage computer cannot be captured by
the RS232 interface. However, if both a PS/2 keyboard and RS232 interface are connected, any data input to a
vintage computer with the PS/2 keyboard will be automatically echoed to the RS232 interface.
KEY SEQUENCE DESCRIPTION
Control-R
Control-S
Control-T
If CR shunt is not in place, pressing these keys, sequentially, will cause reset to
be asserted
Control-C
Control-L
Control-R
If CR shunt is not in place, pressing these keys, sequentially, will cause clear to
be asserted. This is intended to clear the screen of an Apple 1 computer
With the right terminal software on a PC, commands and programs can be automatically loaded into a vintage
computer using this write only interface. Typically the text to be entered, is put into a le on the modern PC.
The format will often be a series of monitor commands that write memory. These les are sent to the vintage
computer using the terminal software’s send le command.
Some vintage computers, such as the Apple 1, have a very limited rate at which they can accept monitor input.
In these cases, to prevent overruns, the terminal software must be congured to delay between characters and
lines. The exact delays required for reliable data transfer depend upon capabilities of the specic vintage com-
puter. I have found that the Apple 1 monitor accepts data reliably with a 20 millisecond per character delay and
a 200 millisecond end of line delay.
page 14
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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