May
2004, Issue 166
Radio
Roundup
MAXSTREAM
9XStream
My
first impression of the 9XStream came when my UPS driver
handed me the 9XStream evaluation kit box. It was a
big box, and I figured it held either a complicated
data radio kit or lots of goodies to support a simple,
well-equipped embedded data radio rig. Before installing
the CD-ROM-based documentation and configuration program,
I rummaged through the evaluation kit to see if I was
going to have to go the Florida room library and meditate
with the 9XStream documentation.
Three
of what seemed to be communications interface adapters
caught my eye. The first adapter pulled from the shipping
foam was pink and imprinted with the word “LOOPBACK.”
Heck, I know what a loopback adapter is. No worries
here, I assured myself.
Then,
I asked myself what I’d do with a loopback adapter in
a wireless network. OK. Next adapter. This black adapter
was labeled “Null Modem Adapter.” I’m batting a perfect
1000 because I can also tell you what a null modem adapter
is used for. Again, I asked myself what I’d do with
one in this environment.
I
shrugged off the self-inflicted questioning and moved
on to the third and final adapter, which was white and
identified as “Null Modem.” The tag on the plastic bag
also pointed out that this adapter was a female-to-female
null modem adapter. Hmm. I pulled out the black null
modem adapter again and noted that both of its interfaces
were male. As you can imagine, I was ignorant at this
point, and this group of out-of-place adapters really
had me swinging. What in the world am I going to be
looping back? I wondered. What am I going to do with
“null modeming” in a set of wireless data radio modules?
Fortunately,
the rest of the parts and pieces made a bit more sense
to me. The following were easily identifiable: a couple
of nine-pin male-to-female signal cables for attaching
to PC serial ports, two 9-VDC wall warts, and a pair
of male and female nine-pin to RJ-45 adapters to allow
the use of Cat 5 cabling as data cable. The neatest
cable I found adapted a standard 9-V battery to the
wall wart power receptacle on the evaluation/ development
board. I figured that the examination of the actual
data radio electronics would give me some clues as to
what to do with those crazy communications adapters.
I
decided to begin by examining a 9XStream evaluation
board. The RS-232/485 circuitry looked standard enough,
as did all of the pinouts for interfacing to the actual
9XStream data radio module.
DIP
switch settings determine if you have to incorporate
parity or run RS-232, two-wire RS-485, or four-wire
RS-485. 9XStream RS-485 termination options are also
DIP switch-selectable. The remainder of components on
the evaluation board consists of a low-power, low-dropout
voltage regulator and supporting circuitry, a configuration
push button, and an ATtiny26 microcontroller. Hmm.
The
9XStreams that I dug out of the box are compact data
radios that operate in the 900-MHz band at 9600 bps.
The 9XStream’s RF circuitry is confined to a shielded
enclosure with an ATmega32(L) being the most prominent
part mounted outside the shield.
After
I assembled the 9XStream radios and evaluation boards,
I connected them to separate PCs in the Florida room.
Instant gratification: the radios worked perfectly together
right out of the box. The next step was to sort through
the 9XStream documentation to try and figure out what
to do with the adapters. The documentation on the CD-ROM
is extremely detailed and complete.
The
9XStream can be programmed using 9XStream-unique AT-type
commands or via the X-CTU program, which is on the CD-ROM.
The AT commands that can be issued fall into four categories:
diagnostic services, networking services, command mode
operations, and serial interfacing. The X-CTU interface
automates the AT command configuration process and includes
extra services like range testing and an ASCII terminal
interface.
While
experimenting with the X-CTU application, I came across
a section in the advanced 9XStream documentation that
solved the communications adapter mystery. The pink
loopback adapter is used to loop received data back
into the transmitter during range testing. Using the
pink loopback adapter converts the stationary remote
radio into a repeater that simply echoes the data sent
from the 9XStream radio you’re walking away with during
the range test. The black null modem adapter is used
to connect the 9XStream’s DCE interface to another target
DCE interface. The white female-to-female null modem
adapter replaces a set of 9XStream data radios and can
be used to connect and test the DTE interface cables
that connect the 9XStream to each respective host.
Now
that everything has been identified and categorized,
what does it take to connect the 9XStream to an embedded
host? The answer is simple: three wires. From the 9Xstream’s
perspective, they are data in (DI) from the host, data
out (DO) to the host, and clear to send (CTS). All else
is automatic. The 9XStream adds a factory-assigned vendor
ID number (VID), a channel number (ATHP), a module address
(ATDT), and a packet serial number (PSN) that identifies
each packet in front of the data received from the host.
A 16-bit CRC is appended to the outgoing packet.
There
are also 9XStream pins that provide optional features
such as power-down, reset, and module status that can
be used by the host and host application. The 9XStream
has a useful range of up to 1500’ with a standard
whip antenna. If your 9XStream radios are configured
with special high-gain antennas, you can obtain signal
ranges of up to 20 miles line of sight. Using the DCE-to-DCE
adapter, I 9XStream-enabled an EDTP Easy Ethernet ASIX
board, which happens to have an on-board PIC microcontroller
supporting a simple three-wire RS-232 DCE interface
(see Photo 3).
|
(Click
here to enlarge)
|
Photo
3—Here’s an example of “drop in” RF. The EDTP Easy
Ethernet ASIX board can now add wireless to its
Ethernet and I²C connectivity resume. All I had
to do to wireless-enable the Easy Ethernet board
was change the data rate in the PIC firmware. |
