QEX – May/June 2010
3
Reprinted with permission © ARRL
David Bern, W2LNX
8809 Cold Spring Rd, Potomac, MD 20854; [email protected]
A PS/2 Keyer: Using a Keyer
Paddle to Emulate a PS/2
Keyboard and Mouse
1
Notes appear on page 8.
Would you like to operate your computer without a keyboard?
How about RTTY or PSK-31 without a keyboard? Now you can.
This article describes my first program-
ming project with a Microchip PIC
®
micro-
controller. The program for this project,
written in C, emulates a PS/2 keyboard and
a PS/2 mouse using a CW keyer paddle for
input.
Note: an earlier version of this article was
published in The 28th Annual ARRL and
TAPR Digital Communications Conference
Proceedings
. The 28
th
Annual DCC was
held in Chicago, Illinois on September
25-27, 2009.
Over the past several years, I became
interested in learning how to program
Microchip PIC microcontrollers and I began
to look for an interesting project. I am an
experienced C programmer, but I knew
nothing about PIC microcontroller program-
ming. My criteria for the project was that it
needed to have a well defined input, a well
defined output, and the circuit needed to
consist solely of a PIC microcontroller with
some light emitting diodes (LED). And,
importantly, it needed to be written in C.
At the 26
th
DCC, Milt Cram, W8NUE
and George Heron, N2APB introduced their
NUE-PSK digital modem.
1
The full details
of the NUE-PSK modem were published
in the Mar/Apr 2009 issue of QEX (NUE-
PSK Digital Modem Enables PSK31 Field
Operation Without Using a PC!), along with
a summary article in the March 2008 issue
of QST. The NUE-PSK modem is a small
device that provides portable PSK31 (and
now RTTY) operation without the use of a
personal computer. It does, however, require
a PS/2 keyboard for entering text. It occurred
to me that it could be more portable if the
large PS/2 keyboard were replaced with a
CW keyer paddle. A PIC microcontroller
would translate CW input sent on the paddle
into the output from a standard PS/2 key-
board. Hence, I found the idea for the project
for which I was looking. I would write a pro-
gram that runs on a PIC, and that emulates
a PS/2 keyboard using a keyer paddle for
input. Later on in the project, I wondered if
it was also possible to emulate a PS/2 mouse
with only two switch contacts and no other
moving parts.
Background
Morse Code
Morse code input is defined in the ITU
recommendation on the international Morse
code and is further described in an article in
Wikipedia.
2, 3
The CW character and word
timings needed for this project are the length
of time of a dash relative to a dot, the length
of time between dots and dashes in a letter,
the length of time between letters and the
length of time between words.
The PS/2 Protocol
The output of a PS/2 keyboard and a PS/2
mouse follow the PS/2 protocol, which was
originally described in the IBM Personal
System/2 Hardware Technical Reference
,
in the sections on the “101 and 102 Key
Keyboard” and the “Keyboard and Auxiliary
Device Controller” sections of the computer
reference manual, respectively.
4, 5
Articles on
the Internet about the PS/2 protocol, the PS/2
keyboard protocol, and the PS/2 mouse pro-
tocol were most helpful.
6, 7, 8
More recently,
an article describing a keyboard-game inter-
face using the PS/2 protocol appeared in
Nuts and Volts
magazine.
9
The physical PS/2 interface, shown in
Figure 1, used for the keyboard and mouse
connectors uses the PS/2 protocol. The PS/2
protocol is a two way synchronous protocol
used to communicate between a host and a
device. (See Note 6.) A host, typically, is a
personal computer and a device, typically,
is a keyboard or a mouse. In addition to a
clock line and a data line, there is a 5 V line
and a ground line. The PS/2 protocol uses
the clock line and the data line for sending
data. The frequency of the clock is within
the range of 10 to 16.7 kHz. Data is sent as
an 11 bit frame, starting with a zero start bit,
the eight data bits, with the least significant
bit first, an odd parity bit and one stop bit.
The device always generates the clock sig-
5
6
3
4
1
2
6
5
4
3
2
1
Male
(Plug)
Female
(Socket)
6-pin Mini-DIN (PS/2)
1 - Data
4 - Vcc (+5 V)
2 - Not Used
5 - Clock
3 - Ground
6 - Not Used
Figure 1 — The PS/2 ports for the keyboard
and mouse on personal computers use six
pin mini-DIN connectors.
