Origa.me

Oh dear, it seems my parallel port LVP programmer was somewhat fragile - I'll skip the details but suffice to say it doesn't work any more. The silver lining to this sad story is that it led me to build a really simple and cheap ICSP (In Circuit Serial Programmer) which connects to the serial port and only uses 3 resistors.

ICSP, as the name suggests, allows programming of a PIC 'in circuit', avoiding the need to constantly take it in and out of the programmer and the subsequent bending of pins. This programmer works with any standard serial port (1) and successfully programs my 16F628 PICs in HVP (high voltage programming) mode giving me an extra pin on PORTB - which is handy. As with the LVP programmer, it draws power for the PIC's main supply voltage (Vdd) from a USB port. Here's the circuit:

And here's a photo of the finished item with globs of "hot glue" (marvelous stuff!) to prevent cable breakage:

Software is IC-Prog - again, a Windows program but it has its own I/O driver for Windows 2000/XP which avoids all the arseing about with GiveIO.sys. As for the hardware settings in IC-Prog, programmer type is "JDM" using direct I/O; all other boxes are unchecked. I have yet to try this programmer with my Linux machine as that has low power serial ports (see 1 below) but it works well on Windows.

1. On my desktop machine, measuring the voltage across pins 5 and either 3, 4 or 7 on the 9 pin D-type serial connector with a multimeter shows just over 10V. On my Linux machine (somewhat akin to a laptop) the same pins show around 5V which seems not to be enough to raise the programming voltage (Vpp) on the PIC to the required level for HVP. I haven't tried it in LVP mode (+5V on PGM) which may work if it happens in the right sequence. It may also be possible to overcome this voltage deficit by boosting the voltage to RS-232 levels using a MAX232 chip but I haven't tried this.