Dual PIC Programmer:

LVP Low Voltage Programming Mods

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Here is how to modify the PICPN to low voltage program suitable PIC's. Later PIC's can be programmed without puttting Vpp on the reset pin. This is sometimes handy for in circuit programming, where the reset circuit won't stand 13V.

You can modify one or both channels. Most people will just want to modify channel 2 for specific in-circuit programming, and keep channel1 (and the socket) for VPP programming control.

PICPN Overlay Drawing

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Diagram of mods for Ch2 LVP

Diagram of mods for 8 pin socket

  • Download and print the circuit and overlay PDF's
  • LVP Circuit Diagram LVP Circuit (ie after mods to both channels)
  • Circuit Diagram Standard (VPP) Circuit (ie before mods)
  • PCB Overlay PCB Overlay
  • Decide which channels to modify.
  • Add a 2k2 resistor from pin7 (LVP) of the programming headers to Pin8 (VSS). This is the RB4 pull down resistor
  • lift the collector leads of Q10(channel1) and Q7(channel2)
  • drill a 1mm hole adjacent to the existing hole, through the blank fibre glass are, and put the collector lead through
  • link the collector lead to pin7 of the appropriate headers
  • Cut the 12V track going to the emitters of Q10,7 and R10,R12
  • link these to VDD (pin8 of headers)
  • Test using an oscilloscope and debug mode: PP06 -debug
  • Note that RB4 is used on 16F628, others use different pins!
  • The same software is used. Versions >1.08 have been tested

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Lennie Reeh reports that he had to use the programmers switched VDD when doing in-circuit programming of 16F628's. Perhaps the LVP mode is only entered at power on?

The LVP pin causes problems to high voltage programming when the devices are blank or just erased. You must ensure that the LVP pin remains LOW during normal programming. Note that once LVP is set off, this isn't a problem, but if you have to erase the device, eg if it is code protected, then the problem comes right back.

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Our ICSP header

The boards use an AMP (tyco) 8 pin MicroMatch header. You can order some with your programmer Buy It Now!

Desc AMP# Farnell# RS#
PCB Female-on-board 7-215079-8 148-593  
Cable Male-on-wire 7-215083-8 149-070  
# VPP Versions LVP Versions
7   RB4/LVP

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Drawings: Circuit and PCB Overlay

LVP Circuit Diagram LVP Circuit (ie after mods to both channels)

Circuit Diagram Standard Circuit (PDF 71k) PCB Overlay (PDF37k)Zip File (Documentation and Hi-Res Drawings) File Formats

Circuit Diagram (PNG96dpi 7k)PCB Overlay (PNG96dpi 40k)

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