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I am confused with how the Low voltage programming mode works on PIC18F2550. I know that PGM pin is pulled high when device enters into programming mode, but can't find in the datasheet about what happens to the MCLR pin in LVP mode and where does it connect with say, PICKit3, or is it kept at supply voltage in programming mode? Also, some sources mention that PGM pin is being removed from LVP mode in some recent devices, instead a 32 bit sequence is sent to put the device in programming mode. I can't find which pin this sequence is sent through, MCLR or PGD? Thanks for the help.

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  • \$\begingroup\$ Take a look at Section 2.6 on page 17. \$\endgroup\$
    – Ron Beyer
    Commented Feb 27, 2020 at 13:08
  • \$\begingroup\$ @RonBeyer Thank you very much, I get it now. For troubled guys of future, to put the device in low voltage programming mode, MCLR, PGM, PGD, PGC all are pulled low in the beginning, then PGM and MCLR are pulled up in that order and then only data transmission and clock begin. Exiting steps exactly opposite of this procedure, pull PGC, PGD low, then pull MCLR low, then pull PGM low. \$\endgroup\$
    – tree_3
    Commented Feb 27, 2020 at 15:29
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    \$\begingroup\$ Welcome to SE/EE. The troubled guys of the future will not consider reading this question in the first place, because it has no answer. So, please, write an answer yourself, and mark it when allowed to. Or, if you think this question is trivial and you should have read the data sheet a bit longer before asking, consider to delete it. -- You might like to take the tour and read "How to Ask" in the meantime. \$\endgroup\$ Commented Feb 28, 2020 at 7:21

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To put the device in low voltage programming mode, MCLR, PGM, PGD, PGC all are pulled low in the beginning, then PGM and MCLR are pulled up in that order and then only data transmission and clock begin. Exiting steps exactly opposite of this procedure, pull PGC, PGD low, then pull MCLR low, then pull PGM low. Additional link on specifics of programming PIC mcus(thanks to @Ron Beyer), see page 17, section 2.6 ->
http://ww1.microchip.com/downloads/en/DeviceDoc/30009622M.pdf

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