September
2004, Issue 170
Multilab
Build
a Z8 Encore!-Based Multipurpose Test Instrument
POWER
SUPPLY
Figure
5 is the schematic diagram of the power supply. Because
of the mixed-signal nature of the project, a number
of voltages were necessary. Both the arb DAC and the
op-amps are connected to the raw ±12-V outputs of the
bridge rectified power supply. The Z8 Encore! and IrDA
transceiver need 3.3 V, which I also used for the CMOS
chips in the PLL and the 24LC256 flash memory. An LM1086-3.3
provides the 3.3-V supply.
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(Click
here to enlarge)
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Figure
5—A multivoltage power supply is needed because
this is a mixed-signal design. A Zener diode provides
an additional –5-V supply, which isn’t shown here
(refer to Figure 1). |
However,
the MAX232, DAC7611, and TC500 need 5 V, so a 7805 is
also required. The TC500 also needs a negative voltage
source, which is provided by a 5-V Zener diode. Maxim
also makes the TC510 with a built-in charge-pump, but
I didn’t spring for this version because I had a negative
supply available.
Z8
FIRMWARE
I’d
used either assembly language or BASIC for every MCU
I’ve worked with over the years. I hadn’t used C language.
Because the Z8 Encore!’s IDE and on-chip debug facility
were tailored to work with the free ANSI C compiler
included with the development kit, I decided it was
time to learn something new.
I
used the serial I/O, I2C, SPI, and floating point/ trigonometric
functions included with the C compiler package. There
is also a library titled API, which handles all of the
timer functions. I used it to some extent, but in some
places, particularly where setting up the timers needed
to be done quickly, I wrote my own faster timer handling
routines.
I
used numerous variables, including a memory array of
256 or more elements for the arb waveform memory, so
I implemented the large memory model in the compiler.
The small memory model uses only the basic 256-byte
register space in the Z8 Encore!. I also had to remember
to explicitly instruct the compiler to use the floating-point
library because the waveform generation, as well as
many of the timing calculations, was done in floating
point. The program used up approximately 60% of the
64-KB flash memory in the Z8F6401.
The
program flow is fairly basic. At reset, all of the necessary
I/O ports are configured properly. Then the RS-232/IrDA
switch is checked to see if the unit is going to be
talking to a PC directly or to a Palm Pilot via the
IrDA link. The applicable UART port is then selected
as the active communication port, and the program enters
a loop awaiting commands.
All
commands consist of a single line of ASCII text containing
three numeric parameters. The first parameter is the
function number (currently one through seven). The meaning
of the other two parameters varies by function. The
only exception is the store waveform command. After
the normal command line, a series of bytes follows.
These are the waveform values themselves.
After
the Z8 has received a complete line, it uses the sscanf
function to parse it into the three numeric parameters.
The first parameter is used with the switch function
to call the appropriate routine. The other two parameters,
which are floating-point numbers, are used to set up
the waveform shape, frequency, pulse widths, and reference
voltage as required by that particular function. Only
in the case of the DC voltmeter function is a value
returned to the PC or Palm Pilot. In this case, a 16-bit
integer is transmitted back to the host where it is
scaled into the correct voltage readout. Table
3 shows the structure of the various commands used
by the MultiLab.
PC
& PALM APPS
Both
Palm Pilot and PC applications are needed to operate
the MultiLab. In the case of the Palm Pilot, I used
AppForge’s MobileVB program, which is designed as an
add-in tool for Visual Basic 6, and allows the Visual
Basic programmer to operate in the familiar Visual Basic
environment. However, it creates a program that will
run on the Palm Pilot.
I
have experience with Visual Basic, so MobileVB wasn’t
too hard to get used to. I wrote an application to handle
the various functions, but, given the time constraints
of the Zilog Flash for Cash Z8 Encore! International
Design Contest, it isn’t too fancy. Photo 1 shows one
screen of the Palm application running in MobileVB’s
PC Emulation mode. However, my digital camera couldn’t
take a clear enough picture of the application running
on the Palm Pilot to show you.
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(Click
here to enalrge)
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Photo
1—The Palm Pilot application program is shown here
running under PC emulation. My digital camera didn’t
take a clear photograph of the Palm’s small screen.
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The
PC application, which was written in Visual Basic 6,
performs a similar function to the Palm Pilot program,
except it can also download arb waveforms to MultiLab.
Photo 2 is a screen shot of the application. Photo 3
shows a sampling of some of the arb’s output waveforms.
Photo 4 shows the MultiLab without its top cover.
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(Click
here to enlarge)
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Photo
2—The Visual Basic PC application acts as the MultiLab’s
front panel. Although it handles the same functions
as the Palm Pilot application, it’s easier to use
because it isn’t limited by the Palm Pilot’s small
screen limitations. |
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(Click
here to enalrge)
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Photo
3—Here are four output signals from the MultiLab
captured by my Tektronix 3052 DPO oscilloscope.
Working clockwise from the upper left you can see
a sine wave with added harmonics, pure sine wave,
square wave, and sawtooth. |
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(Click
here to enlarge)
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Photo
4—Apart from the power supply, all of the MultiLab’s
circuitry fits easily on a vector 8001 prototype
card. The window that allows IR communication with
the Palm Pilot is barely visible under the red-handled
power switch. |
BUILT-IN
ADVANTAGE
Considering
that the Z8 Encore! and C language were completely new
to me, I must
admit that working with the Z8 development board and
software was a pleasure. During the early stages of
the project as I stumbled around with unfamiliar C syntax,
the on-chip debugger was a prayer answered. The MCUs
I’ve used in past projects didn’t have this built-in
function, but now I don’t want to do without it. Overall,
I’m pleased that the project has met my expectations.
