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pull-down resistors R12 and R16 are
copied from the original ICD module.
The series resistors R11, R15 and R17
limit the output current of the host
hardware under short circuit conditions
to a value that is not going to
cause trouble for IC1. D4 protects the
circuit against excessive supply voltage
or reverse polarity. In view of the
intentionally restricted functionality of
this unit some care is necessary, as
D4 may not be able to compete with
an laboratory power adjusted to 30 V
and 5 A.
Analogue inputs RA0, RA1 and RA3
measure the level of the programming
voltage and the supply voltage at the
Reset pin of the host hardware. The
test values are monitored in the development
environment and are displayed
in the “Debugger/Settings/Power”
window. For absolute precision the
voltage divider can be built using 1%
(close tolerance) resistors.
The LEDs D5 to D7 indicate the presence
of the operating voltage, an operation
in process in IC1 or a fault condition.
As in the Microchip ICD2, the
Power LED (D7) is green, the Busy LED
(D6) yellow and the Error LED (D5) red.
Printed circuitboard and
Bootloader
Since the single-sided PCB (Figure 2)
is populated using conventional-size
components with normal wire leads
and is not cramped, construction is
possible inside an hour, even for those
less skilled at soldering. After fitting
the components and making connection
to the host hardware as shown in
Figure 3 the programming voltage on
pin 2 of IC2 should measure in the
region of 12.75 to 13.25 V. Precise
adjustment of the programming voltage
can be made by altering R1 if necessary.
In most cases this should not
be required, since many PICs can tolerate
levels between 12 V and 14 V.
If not already obtained, the current version
of the development environment
MPLAB IDE (version 7.40 at time of
writing) should be downloaded from
the Microchip homepage [1] and
installed. Reply ‘no’ to the question
about installing custom USB drivers, as
the circuit presented in this article
uses the serial interface.
To enable the development environment
to load the PIC Controller IC1
with firmware appropriate to the particular
host processor being used, IC1
must be programmed with a Bootloader.
This has been taken care of
PC
RS232
test and programming module
PIC16F877
+13V
220 Ω
already in the pre-programmed microcontroller
(order code 050348-41)
shown in the component list.
It is also possible to program the Bootloader
into a PIC16F877 oneself. The
Bootloader program BL010101.hex is
part of the development environment
MPLAB and can be found in the file
‘\Programme\Microchip\MPLAB
IDE\ICD2’. People with no access to a
programming device will find in [3] a
simple circuit for the parallel port; this
can be made up on vero board or handwired.
The MPLAB Bootloader is written for
the 16F877. The more recent 16F877A
employs a modified programming algorithm
and therefore requires a modified
Bootloader, available on the Internet at
[5] (scroll down the page until you see
the word Bootloader) and elsewhere.
Using the 16F877A runs a risk, however,
that the Debugger will stop working
if Microchip replaces the Bootloader
in the MPLAB development
environment with a new version in a
future firmware update.
Ready
With the circuit and programmed IC1
chip connected to the PC, the development
environment can be started up.
First off the ‘Debugger/Select
Tool/MPLAB ICD2’ of Debugger type
ICD2 is selected. In the menu ‘Debugger/Settings/Communication’
that follows
the next task is to nominate the
serial interface to which the device is
connected. In the same menu the Baud
rate is set to 57600. A warning ‘ICD-
220
Ω
220 Ω
4k7
4k7
TGT VCC
TGT MCLR
TGT PGD
TGT PGC
GND
100k
Rc
100k
Rb
target system (TGT)
10k
Ra
1
40
39
MCLR
PGD
PGC
VSS
Warn0034: Please ensure that your system’s
serial FIFO buffers are disabled’
appears when the FIFO buffers have
been deactivated correctly — this can
be ignored.
With the command ‘Debugger/Connect’
the development environment
opens communication with the Debugger,
carries out a self-test and displays
the result in the ‘Output/MPLAB ICD 2’
window. Curiously the message
‘MPLAB ICD 2 Ready’ appears even if
the Debugger is not connected.
If no firmware corresponding to the
host processor is present in IC1, the
development environment will suggest
downloading this. If the option ‘Automatically
download firmware if
needed’ has been selected in the
‘Debugger/Settings/Status’ menu, this
download takes place automatically.
During the download time of about a
minute the Busy-LED D6 is lit.
After a renewed ‘Connect’ the development
environment displays the result
seen in Figure 4 with ‘MPLAB ICD 2
Ready’ on the last line. The device is
now ready for use and can now be
used either as a Debugger (menu
choice ‘Debugger/Select Tool/MPLAB
ICD2’ or as a programming device
(menu option ‘Programmer/Select Programmer/MPLAB
ICD 2’).
Practical tips
The sample interface between host
hardware and Debugging Module
shown in Figure 3 using a host processor
of type 16F877 can be applied to all
PIC computers that support the ICD2
11
VCC
32
VCC
PIC16F877
12 13 14
U b = +5V
VSS
31
050348 - 12
Figure 3. Five wires provide the connection from the ICD/ICP module to the target system.
10/2006 - elektor electronics 53