In my opinion, many boards like our board have too
many pushbuttons. The sole intent of designing in the
single pushbutton switch was bootloading control. My first
use of the pushbutton switch during development of the
code for this column was in a debugging sequence. So,
it’s there if we need it for whatever we may need it for.
The PIC32MX795F512L is programmed and
debugged using a PICkit 3, which is attached to our
board’s male five-pin ICSP connector using a six inch
cable assembly terminated by a five-pin DF13 1.25 mm
USB in a Chip
The FT232RL is attached to the PIC32MX795F512L
via its transmit and receive lines.
This module will most likely be
used to communicate with a host
USB device such as a laptop PC.
The only physical
housekeeping we have to do here
is make sure we don’t over-current
the indicator LEDs. The real work
is in the firmware driver. You can
view the FT232RL hardware
details in Schematic 2.
RS-232 is Not Dead
The news of the death of RS-
232 has been greatly exaggerated.
RS-232 interface ICs are not hard
to find, and many modern devices
are equipped with a legacy RS-Like the USB subsystem, the RS-232 subsystem is not
a burden on the hardware side of the fence. According to
Schematic 3, we only need to add five 100 nF capacitors
to the mix.
microSD on a String
A slightly modified version of SparkFun’s OpenLog is
drawn up in Schematic 4. The original intent of the
OpenLog was to simply store the incoming stream of RS-
232 data on the microSD card. However, there are
commands associated with the OpenLog that allow us to
control the microSD card file system.
So, we can choose to use this
microSD card to log data or store data
under program control. The really neat
thing about it all is that the control and
data transfers are done via one of the
microSD the Microchip Way
The “other” microSD card is being fed
from one of the PIC32MX795F512L’s SPI
portals. Like the OpenLog microSD card,
the “other” microSD card can be used to
log data or store data under program
control using Microchip’s microSD card
However, the microSD card under the
control of the PIC32 also has the ability to
hold firmware images that can be
bootloaded into the PIC32MX795F512L.
Jumper blocks are used to set the card
62 August 2015
■ Schematic 3. Setting up an RS-232 hardware port used to be a real pain.
I remember back in the day having to lash up separate receiver and
transmitter ICs that required negative supply voltages. Today's RS-232
interface ICs are a breeze to use.
■ Schematic 2. There's not much to do here as far as the hardware is concerned.
Tasks include filtering the supply voltage and taking care of the indicator LEDs.
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