You'll find three techniques to program a PIC microcontroller
1. Employing usual programming hardware (high volt programming HVP).
2. Low volt programming (LVP).
3. Bootloading.
The very first two approaches make use of the programming port with the PIC microcontroller labeled ICSP (In Circuit Serial Programming).
This port is shared in between the existing pins with the microcontroller and following programming the pins revert back to normal microcontroller operation.
Note: To make ICSP work correctly you must take into account the effects and requirements in the ICSP programmer e.g. for HVP a substantial voltage exists in the Vpp pin (your circuit must be capable to handle the large voltage up to 13V). Also the loading for that other signals PGC and PGD must not be too high i.e. do not put an LED on these pins that employs 20mA should you did the voltage levels would not be higher sufficient at the inputs to the PIC for programming.
It's fairly easy to design for ICSP use by using isolation resistors to regular circuitry and choosing not to utilize heavy loads on these pins.
ICSP delivers 6 connections in the pic ICSP programmer for your board as follows :
VPP (or MCLRn) Programming voltage (usually 13V).
Vcc Energy (typically 5V).
GND Ground (zero volts).
PGD Information usual interface and connection RB7.
PGC Clock normal port and connection RB6.
PGM LVP enable regular interface and connection RB3/RB4.
PIC Micro: Substantial Volt Programming
To use the first technique a hardware interface is required or PIC programmer' to interface among the programming software (normally running on the PC) as well as the PIC chip. This hardware takes its information through the PC via 1 of 3 interfaces either:
* The RS232 COM interface
* The Parallel port
* The USB port
You select the interface you want to utilize after which opt for an suitable PIC programmer. The PC then communicates with the hardware generating the serial (ICSP) signals to translate the PIC hex file into a serial information stream suitable with the target microcontroller.
Be aware: Practically all PIC microcontrollers use the ICSP interface so when you have a HVP you are able to software virtually any PIC microcontroller. e.g. you can program 12F675, 16F84, 16F88, 16F877(A), 18F2550, 18F452 etc.
You will find several programs for programming PIC micos e.g. ICPROG and several several hardware programmers.
PIC Micro: Reduced volt programming (LVP)
LVP is precisely the same as HVP except:
* The Vpp voltage is set to the usual supply voltage.
* The PGM pin indicates programming mode.
Be aware: In this mode it is possible to not make use of the PGM pin for anything else it can be dedicated solely to LVP control.
Devices are manufactured with PGM mode enabled and the only solution to turn off the PGM mode is always to method it applying an HVP programmer.
Note: Some PIC microcontrollers can only make use of the HVP technique because for that LVP strategy you need to sacrifice one particular pin PGM (to tell the PIC Micro either that it can be getting programmed (large volts e.g. 5V) or that it isn't being programmed (0V) ) and some PIC micros only have 8 pins e.g. 12F675. For this chip the PGM pin is not obtainable so HVP may be the only way.
The actual benefit of applying the LVP mode is which you can system many PIC Micros on a board with no having to individually program each and every 1 you could daisy chain every additional micro to a master micro which would then program every a single in turn and this is only feasible since the Vpp signal is really a regular logic level in LVP mode.
PIC Micro: Bootloading
Bootloading makes use of any available interface to load a system into system memory. It requires a bootstrap program to interpret the interface information and translate it into software memory guidelines.
Be aware: Note only the newer devices which are capable of programming their own memory can use this technique.
Normally a serial port is employed for bootloading along with the PIC micro bootstrap program will wait for a set time after energy up listening on the serial interface for any reserved word that tells the bootstrap plan to commence i.e. it listens for sequence of characters that's not usually utilised around the interface
Once it receives this sequence it enters bootstrap mode where a hex file is transmitted for the microcontroller over the interface. It interprets this and programs the memory of the microcontroller after which starts the method.
You will discover two issues with this approach:
1. You have to plan the bootstrap code applying HVP or LVP.
2. It uses up some on the microcontroller resources.
When programed it supplies a convenient way of using the device as you won't have to have programming hardware anymore and a single main gain is that you can re-program a device without the need of undoing the equipment e.g. should you boxed up you project you can still re-program it making use of the serial interface!
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