73 Amateur Radio Today - Free and Open Source Software

The best approach is to get an evaluator
board and development software which allows
the user to write the program in whatever
language is convenient. translate it into
machin e code. and transfer it into an emulator
system which mimics the intended
device. With this scheme. the developer
can write a bit of code. try it out. and confirm
that the routine works as intended by
looking at internal memory and registers. It
is possible to write the code blind. manually
transfer it into an EPROM. then into the
devi ce via bootstrap mode. but that makes
de bugging very difficult- much like building
a mechanical machine. we ldi ng
the covers on . then trying to figure
O UI it s beh avi or by whether t he
wheels tum!
Fortunately. vendors such as M otorola
ma ke available freeware as­
semblers which take the English-language
source code. convert it into the
machine-readable objec t code. and
put it into file transfer formats suitable
for down loading. (Motorola uses
the "S 19" format.]
Also. Motorola markets low-cost evaluation
and programmer boards-a-these ca n be
used to emulate and program single-chip
mi c ros. With the " M68H C05 PGM R"
board. for example. small programs can be
downloaded into the 'C8 device's internal
RAM and executed without having to program
the on-chip EPRO:-A. Once the routine
is verified. it may be programmed (by
the same board) into the MCU and used as
a building block by other routines. With
careful strategy. qui te a long program can
be developed chunk- by -chunk without
need ing fancy tools. My programmer board
(bundled with some pretty good software)
cost me about $68 .05 (US) three years ago
and I believe it is still available.
Ask around at the computer e1 ub or local
college and look in the ads in magazines
such as Midnight Engineering and Circuit
Cellar for possible development bo ard
candidates. If the price for a good system
is too steep (they can run a couple of hundred
dollars) for one budget. consider finding
a buddy (or buddies) to split the cost
with. Not only do you get access to a
system at less cost. but if you share your
experiences. it makes the learning curve a
lot easier!
Hardware Desc ri ption
The circuitry for the Kendraboard fits on
a small single-layer 2.S- x 4.S- printed circuit
board (same size and sha pe as the
Julieboard ). It is a very low-tech board
which is well with in the fabri cation abilities
of the average ham. I made mine using
an "ironed-on" reversed-image photocopy
as an etch resi st! My design objectives
were simple: lowest possible density for
ease of home fabrication. me chanically
compatible with the Julieboard. and capable
of futu re expansion with the existing
design.
"If the price for a good system is
too steep (they can run a couple
ofhundred dollars) for one budget,
considerfinding a buddy (or buddies)
to split the cost with."
Board logic is very simple: it consists
of a Motorol a MC68HC70SC 8 sing lechip
microcomputer (MCV) and its support
circ uitry. The micro itself provides all
operational functions. exce pt for master
clock generation. (It was easier to fit in a
small clock oscillator module than the discre
te oscillator components and I didn 't
want to spend a lot of time making them
fit). The ' C 8 was chosen becaus e an
MC68HCOSEVM evaluation board was on
hand and the chip features:
-7.7K bytes EPROM (or OTP).
- 176 bytes RAM .
-24 bidirectional TIL 110 lines.
-7 input/s pecial purpose TrL lines.
-Serial (ASCII) communicatio ns interface.
-Serial (binary) peripheral interface.
-Easy-to-use 4Q-pin DIP package.
This device is considerably more powerful
than what this application actually requires.
but I wanted to pro vide for future
growth.
The series resistors are used as a buffer
between the "outside world" and the MCV
for ESD and as an aid to EMI suppression.
The pull up resistors are needed to define
input levels for idle 110 pins [this is tmpor-
Photo C. Kendraboard and Julieboard. (Photo by Sandy VE3AAC. J
14 73 Amateur Radio Today- August. 1994
taut for CMOS devices such as the ·C8).
All 110 connectors. exce pt fo r one. a
male or female DB2S. are 0.100 frictionlock
SIPs and are intended to be used with
matching housings loaded with c ri mp terminals.
The DB25 can be wire-wrapped for
plug-in compatibility with the Julieboard.
either via a DB 2S/ribbon cable "backpl
ane" a s a female. o r directly to the
Ju lieboard OB2S as a ma le. The serial
EEPROM is a future item for when I want
to do nonvolatile channel storage and clock
frequency error calibration. Presently. the
software does not support the EEPROM,
so it may be left out. if desired.
Like the Julieboard. supply vo ltage
input can range from about
+7VDC to + 12VDC. and is protected
against reverse-polarit y damage.
Soft ware Description
In orde r to simplify the software
as much as possible for the initial
version, BCD thumbwheel switches
were used for frequency control and
display. IA keypad and LCD display could
have been implemented. but the software
req ui red would have been much more complicated.I
To drive the DDS. the software
must perform these functions:
-Set up the microcomputer internal registers.
-Rcad the thumbwheel swit ches di git by
digit.
-00 a BCD-tO-binary conversion.
-Send the binary data to the DDS chip.
Se t Up the Micro: The 110 lines used
fo r the BCD di git "commons" and DDS
co ntro l arc set up as outputs. while the
BCD read-back lines are set up as inputs.
Unused 110 lines are configured as inputs
and are pulled HIGH by the board pull-up
resistors. Other processor functions (SPI.
SCI. timer. etc.) are not presently used. but
will be used in the future. At that time,
code will have to be added to initialize
these items. Once the micro has been initialized.
con trol passes to the BCD thumbwheel
switch read -routine.
Reading Ihe BC D T h umbwheei
Swuches: Each BCD switch consists of a
COM terminal and four output bits which
are connected/disconnected to the COM
terminal. depending on code. The required
switch function is:
Code: • 4 2 1
0 01' 011 011 011
1 011 011 011 011
2 011 011 011 011
3 011 011 011 011
4 011 011 011 011
5 011 011 011 011
e 011 on 011 011
7 011 011 011 011
• 011 011 011 011
9 011 011 011 011
The output bits are paralleled via diodes:
The cathodes go to the individual 8-4-2-1