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PIC Micro hardware programming methods.
There are three ways to program a PIC microcontroller
- Using normal programming hardware (high volt
- Low volt programming (LVP).
The first two methods use the programming port of the PIC
microcontroller labeled ICSP (I
This port is shared between the existing pins of the microcontroller
and after programming the pins revert back to normal microcontroller
make ICSP work
correctly you have to consider the effects and requirements of the ICSP
programmer e.g. for HVP a high voltage exists at the Vpp pin (your
circuit must be able to handle the high voltage - up to 13V).
Also the loading for the other signals PGC and PGD must not
too high i.e. don't put an LED on these pins that uses 20mA - if you
did the voltage levels would not be high enough at the inputs to the
PIC for programming.
It's fairly easy to design for ICSP use by using isolation resistors to
normal circuitry and choosing not to use heavy loads on these pins.
ICSP provides 6 connections
from the pic ICSP programmer to your board as follows :
|VPP (or MCLRn)
||Programming voltage (usually 13V).
||Power (usually 5V).
||Ground (zero volts).
|PGD - Data
||usual port and connection RB7.
|PGC - Clock
||usual port and connection RB6.
|PGM - LVP enable
||usual port and connection RB3/RB4.
If you are not using low volt programming
then ignore this pin and disable LVP when
programming the chip.
use the first method a hardware interface is needed or 'PIC programmer'
to interface between the programming software (usually running on the
PC) and the PIC chip. This hardware takes its information
from the PC via one of three interfaces either:
- The RS232 COM port
- The Parallel port
- The USB port
You choose the interface you want to use and then choose an appropriate
PIC programmer. The PC then communicates with the hardware
generating the serial (ICSP) signals to translate the PIC hex file into
a serial data stream suitable for the target microcontroller.
all PIC microcontrollers use the ICSP interface so once you have a HVP
you can program virtually any PIC microcontroller. e.g. you can
program 12F675, 16F84, 16F88, 16F877(A), 18F2550, 18F452 etc.
There are several programs for programming PIC
micos e.g. ICPROG and many different hardware programmers.
PIC Micro: Low volt programming (LVP)
Usually you will not want to use LVP it is a specialized operation that is not normal for standard use - so disable it.
LVP is exactly the same as HVP except:
In this mode you can not use the PGM pin for anything
it is dedicated solely to LVP control.
- The Vpp voltage is set to the normal supply
- The PGM pin indicates programming mode.
are manufactured with PGM mode enabled
and the only way to turn off the PGM mode is to program
it using an HVP programmer.
PIC microcontrollers can only use the HVP method since for the LVP
method you have to sacrifice one pin - PGM - (to tell the PIC
Micro either that it is being programmed (high volts e.g. 5V) or that
it is not being programmed (0V) ) and some PIC micros only have 8 pins
12F675. For this chip the PGM pin is not available so HVP is
the only way.
The real benefit of using the LVP mode is that you can program several
PIC Micros on a board without having to individually program each one -
you could daisy chain each extra micro to a master micro which would
then program each one in turn - and this is only possible since the Vpp
is a normal logic level in LVP mode.
PIC Micro: Bootloading
Bootloading uses any available interface to load a program into program
memory. It requires a bootstrap program to interpret the
interface data and translate it into program memory instructions.
only the newer devices that are capable of programming their
own memory can use this method.
Typically a serial port is used for bootloading and the PIC micro
bootstrap program will wait for a set time after power up listening on
the serial port for a reserved word that tells the bootstrap program to
start i.e. it listens for sequence of characters that is not normally
used on the interface
Once it receives this sequence it enters bootstrap mode where a hex
is transmitted to the microcontroller over the interface. It
interprets this and programs the memory of the microcontroller and
then starts the program.
There are two issues with this method:
- You have to program the bootstrap code using
HVP or LVP.
- It uses up some of the microcontroller
Once programed it provides a convenient way of using the device as you
won't need programming hardware anymore and one major benefit is that
you can re-program a device without undoing the equipment e.g. if you
boxed up you project you could still re-program it using the serial
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