Windows XP support is experimental. See under the heading "Known Problems" for more information.

SimplePicProg is a low voltage in circuit programmer. It only requires a few components to build, and does not need a power supply. It does not require a printed circuit board or a strip board for construction. It is the only passive parallel port PIC programmer I know of that works with long cables.

The P16PRO40 is a popular low cost PIC programmer. The P16PRO40 is capable of programming most PIC chips. It is available from several online retailers for around $US20

Both programmers connect to the parallel port. The parallel port must be located at port number 0x378.

Programming the 12f675:
The 12F675 may only be programmed in high voltage mode using the P16PRO40 programmer.
You must save the value of OSCCAL and the Bandgap calibration bits before erasing. OSCCAL and the Bandgap calibration bits will have to be restored to their original value when reprogramming these chips. See the Microchip data sheets for more information.
Reading/verifying may fail if the MCLR configuration bit is cleared. Program the configuration word from a separate hex file if you need to clear the MCLR configuration bit.

Programming the code protect (CP) configuration bits (all devices):
Programming the CP bits will disable further reading of the chip. This will cause verifying to fail after the code protect bits are enabled. If you want code protection turned on, first program the device without code protection and then program the CP bits from a separate hex file.

For more information on Intel HEX file formats see Microchip document DS91026A.

1. Connect the programmer to the parallel port (plug the DB25 adapter directly into the parallel port)
2. Type 'fpp' - this will display the format of the command line arguments.
3. Type 'fpp lvp -t' - this will check if the software can communicate with the programmer
4. Connect the programmer to the PIC circuit
5. Apply power to the PIC circuit
6. Type 'fpp lvp device_name -i' to display the device id of the chip. The command should succeed without any error messages.
   
7. You are now ready to use the programmer.

The software has two different options for the SimplePicProg programmer: "lvp" and "lvp_fast". The latter uses shorter clock cycles and may be used with cables less than 2 meters in length.

With the SimplePicProg programmer your circuit must be designed to accommodate the programmer:

1. The MCLR/VPP pin should be pulled up to Vdd with 39K
2. The LVP/PGM pin should be grounded with 120K
3. Construct the filter circuit on PGMCLK and PGMDATA as shown on the circuit diagram.
4. You may use the PGMCLK and PGMDATA pins in your circuit, however the load resistance on these pins cannot be less than 270K. (The load resistance cannot be significanly higher than 270k either because the leakage current of the PIC inputs.) With the 18f452 you should dedicate the PGMCLK and PGMDATA pins to the programmer if possible.
5. The voltage supply of the PIC chip must be between 4.75 and 5.25 volts
6. Do not forget to bypass the power supply with a 0.1uF ceramic capacitor. Place the bypass capacitor as close to the chip as possible.

1. Connect the P16PRO40 programmer to the parallel port, make sure the programming socket is empty.
2. Apply power to the programmer.
3. Type 'fpp' - this will display the format of the command line arguments.
4. Type 'fpp p16pro40 -t' - this should succeed and both the red lights on the programmer should be now off.
5. Insert the chip into the programmer.
6. Type 'fpp p16pro40 device_name -i' to display the device id of the chip. The command should succeed without any error messages. (The 12f675 has no device id, if you are using the 12f675 skip this step.)
7. You are now ready to use the programmer.

When using the P16PRO40 always remember the following:

1. Insert the chip into the programming socket only when the green led is on and both red leds are off.
2. Remove the chip immediately after programming. Do not turn off the computer while the P16PRO40 is turned on and a chip is in the programming socket.

The PIC device's programming pins (PGM, MCLR, PGCLK, and PGDATA) have schmitt trigger inputs. The maximum low input voltage on these pins is 0.2 VDD (1V) and the minimum high input voltage is 0.8VDD (4V). The open collector outputs of the parallel port satisfy these requirements.

The PC parallel port inputs are TTL level compatible. TTL inputs have a maximum rise time of about 1us. The series resistors together with the cable capacitance create rise times that well exceed this limit. The 2n7000 logic level mosfet and the BC547 transitor is used to increase the rise time of the input to TTL specifications.

The 220R resistor on the ground line provides protection to the computer by limiting current flow.

It is essential to connect all ground lines as shown on the circuit diagram. It is also essential that you use a ribbon printer to connect the programmer.

The internals of SimplePicProg

SimplePicProg circuit diagram

Programming may fail intermittently under Windows XP with the following error message: "Error while writing to the parallel port: ..." This may be caused by Windows trying to access the parallel port while the programmer is active. This problem appears to be dependent on how Windows XP is configured. On some computers this never occurs; on others it happens frequently.

Here is a list of suggestions that may help:

1. The following registry entry will stop Windows XP checking for new printer connections:
   [HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Parport\Parameters] "DisableWarmPoll"=dword:00000001

2. Try disabling the Windows parallel port device driver. On some computers this may make the parallel port inaccessible.

3. Disable the parallel port on the motherboard and install an old non plug and play parallel port ISA card. Disable the Windows parallel port device driver. This will only work on older computers with ISA slots.

Any software that bypasses the Windows parallel port driver and writes to the parallel port directly is likely to suffer from the same problem. At this time I know of no other parallel port PIC programming software that runs under Windows XP and uses a proper parallel port device driver.

When using the SimplePicProg in circuit programmer, programming or verifying may fail occasionally with the 18f series chips.

I haven't been able to reliably reproduce this problem. If you find a solution to this problem, please contact me.