Hello, The link at the foot of this post leads to a draft schematic for a simple PIC programmer that I would like to share. For want of a better name I am calling this Yet Another In-Circuit Serial Pic Programmer (YAPP). The reason for reinventing the wheel was because I couldn't find a PIC programmer circuit (or even a commercial product) that quite did what I wanted. The main design feature is that it self disconnects from the target circuit so it can be left attached during development, without any need for moving jumpers, switches, plugging / unplugging etc. All phases of chip program/verify/reset/run are under software control using David Tait's excellent FPP programmer software. The design should work with any of the PIC's supported by FPP, but has only been tested it with PIC16C84, PIC16F84 & PIC16F628. I have tried to keep the circuit as simple as possible without sacrificing reliability. The frustration of getting some of the 'minimalist' designs to work reliably was one of the reasons for designing my own programmer in the first place. Connection to the PC is via the parallel port (currently I am using a 5m cable). Connection to the target circuit is via test clips, or whatever suits best. The programmer will also supply 5V to the target circuit. In this case there are two options: a permanent supply (via 5Vout), or supply *only* during PIC read/writes (via 5Vswitched), i.e. this signal is switched OFF during 'run' mode. Alternatively, if the target has its own 5V supply, it would be preferable to only connect through the ground supply line (VSS) and have the target power itself. The programmer will still have control over the target via the MCLR line. If the '5Vswitched' signal is not required, then the whole circuit around the TIP42C becomes optional. The programmer requires at least a 13V dc power supply (currently I am using 13.8V). The 7805 regulator is mounted on a small heat sink. This aspect may need beefing up for higher supply voltages and/or target circuit loads. The design is intended to drive PIC peripherals connected to RB6/RB7, and has been tested with LEDs connected to either supply rail via 1k resistors, however it is possible that the 74LS244 may have trouble with larger loads so please bear this in mind. Also beware that 13V will be applied to the MCLR pin. Therefore if this pin is configured as I/O (RA5), the circuitry connected to RA5 must both *allow* and *tolerate* the 13V in order to avoid damage to either to the programmer or the target. If the MCLR pin is configured as reset input (i.e. it needs to be held high during operation) the target circuit can incorporate the resistor/diode pull-up as shown on the schematic. To check the programmer before using it in earnest, FPP has a test mode - please use it! Next step should be with a PIC chip out of circuit. If FPP reports "Failed to program", try just to program the ID value with an arbitrary number, i.e. don't select code, data or config. If this works then you will know the circuit is basically ok, but there could be problems causing data corruption during the longer programming cycle for a large program. One gotcha to watch out for is that the PIC will be held in RESET while connected to the programmer until FPP is run *and* the 'RUN' button is clicked. i.e. if FPP is not running (or even the PC is switched off), then neither will be the PIC. The schematic shows the programmer 'as built'. It would certainly be possible to replace transistors with equivalents, etc., but what is presented is a known working design. I'll write up some proper notes with a circuit description later when I have more time. In the meantime I am hoping some people might find it useful enough to build and test the design (and report their results to me). If you don't know which way round to put the transistors (or in fact any of the components) please check with someone first, because afterwards it will be too late. None of the components are *supposed* to get hot. ;-) The programmer schematic is here: David Tait's FPP can be found on his home page, here: The FPP settings I am using are here: A zip file, with the schematic, FPP settings, and my notes is here: (c) Bernard Boudet, 2002. I really think this should go without saying, but... DISCLAIMER: No warranty implied. Circuit may contain errors, may destroy the PIC and/or PC, could give new meaning to the error message "LPT1 on fire" - if it does, I told you so. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads