AN589 is microchip’s application note for a parallel port pic programmer circuit which I chose as I wanted something reliable to get up and running quickly.
It is really quite a simple circuit and its main objective is to provide ICSP connections to your pic microcontroller.
Here is the pcb version (click to enlarge):
Note: That the PGM signal is not provided – it’s not really necessary anyway as you can turn off PGM mode by programming the chip. For first use of a chip you will need to pull the PGM line low as PGM is enabled by the manufacturer.
PIC Programmer Circuit diagram
Click on the following diagram to open it as a PDF document.
Disclaimer : If you build this circuit you must double check each connection to the parallel port cable to avoid damage to your computer. This includes checking for shorts between each pin at the parallel port on your circuit. For initial testing it is best if you use a spare (old computer). Building this project is your own responsibility and I can not be held responsible for any damage to your computer.
It has a few modifications that are useful and easy to do:
- Transmission line termination – lets it work over a long cable.
- LM317 voltage regulator to get 11.6 volts and protect the circuit
- Power supply steering diode (stops you reverse connecting the supply).
- Changed LM340-5 to 3pin 100mA LM78L05.
- ICSP connector.
- An LED to show that power is applied.
- Changed 74LS244 to 74HCT244 because I had one handy!
- Standard 10k resistors instead of 2k – just easier if they are all the same.
Transmission line termination
The transmission line termination lets you use the pic programmer circuit at the end of a long cable – I am using a normal parallel cable ~6 feet long. If you want to know more about transmission line terminations then follow this link.
When I first tried to use it I got all kinds of random results so it is worth adding the termination.
Power supply regulators
The LM317 saves you needing an accurate bench power supply – you can use a dc power block – anything that supplies more than about 15V dc. If you don’t use a 317 it’s just too easy to accidentally apply the wrong voltage by turning the dial on a bench supply and frying your microchip. Using the 317 lets you put up to 35V into it (you shouldn’t but you can).
Note: the LM317 and LM78L05 are standard components and are easy to find.
For more detail: A pic programmer circuit based on AN589