60 September 2013
power to the four-bit dual-supply bus transceiver’s VCCB
pin which disables the SN74AVCH4T245’s B portal. If the
embedded host is not operating with 3.0 volt logic levels,
the Five-In-One’s onboard power system must be isolated
and disabled. This is easily done by removing the power
With the power jumper
absent, the output of the
MCP1703 and the AA battery
pack are removed electrically
from the development kit
circuitry. Power must be applied
to the ETRX357 via the male
headers. Embedded development
mode allows us to attach a
microcontroller host running at
3. 3 volt logic levels. The ETRX357,
light sensor, and temperature
sensor are forced to adhere to the
logic level and power rail of the
host microcontroller. Telegesis
Terminal cannot be used as a tool
on the Five-In-One side of the
connection when the Five-In-One
is configured for embedded
Preparing the Combined
Interface device for PC use is a
no-brainer. Simply plug the
Combined Interface device into
the host PC’s USB port. However,
rigging the Combined Interface device for embedded
development requires a bit more work. Refer to Photo 4
as I lay out the steps involved with preparing the
Combined Interface device for embedded development
The first order of business is to isolate the CP2102.
The isolation of the CP2102 provides direct access to the
ETRX357’s signal and power pins. Isolation of the CP2102
involves cutting the TXD, RXD, RTS, CTS, and power
traces near the CP2102. At this point, the ETRX357 signal
lines are no longer electrically connected to the CP2102.
To avoid crazy things that happen to unused active
components that remain powered, the CP2102’s power
input was also isolated. So, now we have a CP2102 that
has no power or signal connections, and an exposed
ETRX357 signal interface.
Figure 1 represents the relationship between the
Digilent six-pin connector cable and the embedded
interface found on a Digilent Cerebot MX3cK
microcontroller board. The layout shown in Figure 1 has
been applied to both the Five-In-One and Combined
Interface device embedded development mode interfaces.
As you can see in Photos 3 and 4, I’ve either
appropriately plugged or soldered the color-coded six-pin
cable connector wires to realize the embedded Five-In-One and Combined Interface device interfaces,
■ Photo 4. Note that I did not remove the CP2102. I simply “isolated” its signal
and power pins. Once isolated, I tapped into the ETRX357’s signal and power
via the isolated connections.
■ Photo 5. Here is the Combined Interface device after its embedded development
mode modification. The Digilent six-pin connector cable is a female-to-female
type. The Combined Interface device embedded interface must be male.
The female-to-male conversion is done using an extended male header.
■ Figure 1. I sacrificed a Digilent six-pin cable
connector to form the embedded host interface
for our Combined Interface device.