© Gooligum Electronics 2015
www.gooligum.com.au
Baseline and mid-range PIC training and dev board operation guide
Page 5
Plug your PICkit 2 or PICkit 3 programmer directly into the
ICSP
socket, with the arrow on the
programmer aligned with the arrow on the PCB (indicating pin 1).
You would normally use the PICkit 2 or PICkit 3 to power the training board. These programmers can
supply up to around 30 mA. If you need more current than this (up to 1 A), or if you wish to use the
training board without having a PICkit 2 or PICkit 3 attached, you can connect a regulated power supply
to the
DC power
socket.
This socket accepts a standard 5.5 mm barrel DC plug, with a 2.1 mm positive centre pin.
Note that there is no voltage regulator on the training board. A diode offers polarity protection, also
dropping the supply voltage by at least 0.6 V. Since most baseline and mid-range PICs (including those
used in the Gooligum tutorials) will work with a supply voltage of up to 5.5 V, you can safely use a power
supply of up to 6 V to power most
3
PICs with this training board – but it must be regulated!
A good choice for an external power supply is a 5 V regulated unit, which will supply around 4.3 V (after
the diode voltage drop) to the PIC.
The
LEDs
are connected, via jumpers and 330 Ω resistors, to PIC pins as marked on the circuit board.
Various PICs use different names for the same pin. For example, pin 2 of socket U2 is referred to as
GP5
if you plug a 12F509 into that socket,
RA5
if you plug in a 16F684, and
RB5
if you use a 16F506. For
that reason, the LED connected to that pin is labelled ‘
GP5 / RA5 / RB5
’
. On the other hand, pin 7 is
called
RC3
on all 14-pin PICs, so the LED on that pin is labelled simply ‘
RC3
’.
LEDs are available on all output pins except
RC4
and
RC5
.
To enable (connect) an LED, simply close its associated jumper.
Pushbutton
switches
are connected to
GP/RA/RB2
and
GP/RA/RB3/
MCLR
via 1 kΩ isolation resistors.
They are
active low
: they will pull the input pin low when pressed (the isolation resistors ensure that the
PIC won’t be damaged if a button is pressed while the pin connected to it is configured as a high output).
The inputs are normally held high, while the switch is open, by either an external 10 kΩ pull-up resistor,
or an internal weak pull-up. Each external pull-up resistor is enabled by closing its associated jumper.
A 10 kΩ
potentiometer
and light-dependent resistor (
LDR
, or CDS photocell), forming one leg of a
potential divider, are available as analog voltage sources. Either can be connected, via jumper JP24, to pin
AN0 / CIN+ / C1IN+
, to act as either an ADC or comparator input.
A
second LDR
can be connected, via jumper block JP25, to ADC input
AN2
or comparator inputs
C2IN+
or
CIN- / C1IN-
.
The board includes a 32.768 kHz
oscillator
, implemented with a watch crystal and CMOS inverter. Its
buffered output can be used to drive Timer0 (in counter mode), by using JP22 to connect it to the
T0CKI
pin. It can also be used as an external signal to drive the processor clock, via jumper block JP20.
In a real PIC application, if you needed a 32.768 kHz clock, you’d be more likely to simply use a watch
crystal with the PIC’s internal oscillator. The training board includes a second 32.768 kHz crystal (with
load capacitors), which can be connected to
OSC1
(on one side) via JP20 and to
OSC2
(on the other
3
some PICs (mostly ‘LF’ variants) will only tolerate a supply of up to 3.6 V- you should limit your external power
supply to no more than 4 V if you are using one of these devices
