A PW1-928 transmit sequence is initiated when the
PIC’s UART is found to contain a received byte. The PIC
enters transmit mode and the SX1272 is put into the
“prepare to transmit” mode. Received data that is driven
through the PIC’s UART is loaded into a different 64-byte
FIFO for the 10 mS it takes the SX1272 to enter a stable
ready state. When the SX1272 is deemed ready, up to 15
bytes of data are transferred from the transmit FIFO,
formatted, and written to the SX1272.
Following the transfer of data from the transmit FIFO
to the SX1272, the transmit command is issued and the
SX1272 responds by transmitting a packet. The
transmission process takes approximately 15 mS. While
the transmit process is in progress, the PIC continues to
read its UART and transfer any new data to the transmit
FIFO. Data in the receive FIFO will be fed out through the
UART during transmit, but new incoming packets cannot
be processed until the transmit process has completed.
At the end of a transmission, if there is still any data in
the transmit FIFO, another read FIFO/format/transfer/start
transmit sequence is triggered. If the transmit FIFO is
empty, the PW1-928 reverts to the receive mode.
Each PW1-928 is capable of being addressed using a
four-bit (1 of 16) group address and a four-bit channel-group identifier. The group address and channel-group
identifier addressing elements are
combined into a single
programmable ID byte.
Each PW1-928 also contains a
unique 32-bit serial number which
is factory programmed into the
PW1-928’s internal EEPROM area.
The PW1-928 serial number can be
accessed by the host
microcontroller via its RS-232 serial
interface. This access to the 32-bit
serial number allows the PW1-928
factory serial number to be used by
the host application as a unique identifier.
The PW1-928 RF Data Transceiver
Module Dev Kit
The PW1-928 module attaches easily to any
microcontroller that is equipped with an embedded UART.
However, if scratch building a PW1-928 host is not in the
design cycle, bringing up a PW1-928 with its development
kit is the easiest alternative option. The official Lemos
International PW1-928 dev kit is shown in Photo 3.
The PW1-928’s component details are graphically
illustrated in Schematic 1. Basically, the PW1-928 dev kit
main board provides a place to mount a PW1-928
transceiver module plus its antenna, a regulated 3. 3 volt
power supply, jumper access to all of the PW1-928’s
indication signals, and a 3. 3 volt compatible serial
interface. Power for the PW1-928 dev kit can be sourced
by the kit’s onboard nine volt battery receptacle or via
header pins on the dev kit main board. Note that the dev
kit’s UART interface is composed of discrete transistors.
There are also LEDs attached to the PW1-928 indication
Turning the PW1-928 Knobs
Figure 3 augments the information provided by
Schematic 1. If we wanted to connect our PW1-928 dev
kit directly to a host PC’s native RS-232 port (good luck
finding one), we would use the PW1-928 RS-232 signals
and ground associated with the dev kit’s JP1 interface. In
this case, we are going to interface our PW1-928 to a
terminal emulator running on a PC. Since my brand new
Dell does not present nine discrete serial port pins in the
April 2017 57
■ FIGURE 3. This layout complements the PW1-928 dev kit
■ FIGURE 4. You can get this cable from
Digi-Key using part number 768-1015-ND.
If you prefer to use Mouser, order part