There is no simpler way to do this than through its EUSART.
If you focus just above the PIC18LF4620 in Photo 2, you’ll
see an assemblage of ceramic capacitors surrounding a
MAX3221 RS-232 converter IC (U5) that just happens to be
attached between the PIC’s EUSART and the outside world.
Just to the right of the MAX3221 lies the 3. 3 volt
regulator area which is built around an LP2981 (U2). The
LP2981 is rated for a maximum input voltage of 16 volts
and is a good choice for this design as the PICDEM Z host
board can power itself from a standard nine-volt battery or
the Microchip PTF0905I power brick.
Photo 3 is a fly-over shot of the 12-pin MRF24J40MA
host interface connector. As you can see in Figure 2, not all
of the 12 available connections are put to use. An
interesting point in Figure 2 is the use of MISO and MOSI
instead of SDO and SDI. Most Microchip documents will
reference the SDO/SDI combination which (when
translated) means Serial Data Out and Serial Data In,
respectively. In Figure 2, MISO — which is short for Master
In Slave Out — is synonymous to Microchip’s SDI, while SDO
is French for MOSI (Master Out Slave In). SPI portal
connections work just like direct-linked RS-232 connections.
The output of Node A must connect to the input of Node
B, and vice versa. That is the Master node’s MOSI signal
must route to the Slave node’s MISO, and the Slave’s MOSI
must feed the Master’s MISO.
The SPI signals that are used to converse with the
MRF24J40MA are shared by a Microchip TC77 thermal
sensor (U3) which can be partially seen in the lower portion
of Photo 3. The MRF24J40MA is selected via pin 6 of the
12-pin PICDEM Z host connector. I/O pin RA2 of the
PIC18LF4620 is used to select the TC77. Only one SPI slave
device can be selected at any time.
A full view of the PICDEM Z host board is under the
lens in Photo 4. A couple of user-accessible LEDs and
pushbuttons are present to allow the designer to simulate
inputs and view output status. That’s the drill on any
Without going into the PIC18LF4620 circuit details, we
now know that the MRF24J40MA moves data between
itself and the PIC18LF4620 using a standard four-wire SPI
portal. We also know that there is a TC77 thermal sensor
that shares the four-wire SPI connection. If we require
them, a standard RS-232 port, a set of pushbuttons, and a
pair of LEDs are available to us. I purposely didn’t post a
PICDEM Z host board schematic as you can get a complete
one by downloading the PICDEM Z Demonstration Kit User
Guide from the Microchip website.
Let’s Mix It Up
Okay. We have the lowdown on the MRF24J40MA. We
also have a very good idea about how the PICDEM Z host is
put together as it is based on a general-purpose
PIC18LF4620. It’s time to meld the radios to the host
boards and transfer some data.
The reason we’re here is to gather enough information
to enable us to use a microcontroller like the PIC18LF4620
to put some MRF24J40MA 802.15.4 radios on the air. So,
PHOTO 4. This is a view of the complete PICDEM Z host
board. The normal complement of pushbuttons and LEDs make
up the rest of this development platform.
PHOTO 5. The PICDEM Z host/MRF24J40MA module
combination you see here is waiting for some radio driver
firmware. Actually, there is a pair of these waiting to be
programmed. One host will eventually be programmed as a
PAN Coordinator and the other as an End Device.
the first order of business is to mate the PICDEM Z host
board and the MRF24J40MA module which I’ve done in
Photo 5. To be able to form a network, I created another
MRF24J40MA node by loading a second PICDEM Z host
SERVO 04.2010 51