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projects:hi-pi [2015/03/25 12:07] – [Schematic] darronprojects:hi-pi [2017/03/23 05:34] (current) – [Appendix] darron
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 Low voltage programming in-circuit is preferable but a high voltage programmer Low voltage programming in-circuit is preferable but a high voltage programmer
 is sometimes a requirement for older parts which offer no low voltage mode, or is sometimes a requirement for older parts which offer no low voltage mode, or
-to reset a device which has low voltage programming mode disabled in it's+to reset a device which has low voltage programming mode disabled in its
 configuration bits. configuration bits.
 +
 +=== News ===
 +
 +A bug may occur with this circuit in certain situations, please refer to the
 +appendix.
  
  
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 {{:projects:hi-pi.png?200}} {{:projects:hi-pi.png?200}}
  
-The TELCOM driver will produce something close to 15V on it's output when activated, it's important to be careful with wiring here and appreciate that this is a dangerous voltage for something like a Raspberry Pi. Be careful when connecting the input pin.+The TELCOM driver will produce something close to 15V on its output when activated, it's important to be careful with wiring here and appreciate that this is a dangerous voltage for something like a Raspberry Pi. Be careful when connecting the input pin.
  
 Note: This is version 1 of Hi-Pi, version 2 will appear here later which will add some small improvements. Note: This is version 1 of Hi-Pi, version 2 will appear here later which will add some small improvements.
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 PGDI=6 PGDI=6
 # PGM # PGM
-PGM=255+PGM=-1
 </code> </code>
  
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 Because this is an out of circuit programmer, we will now need to remove Because this is an out of circuit programmer, we will now need to remove
-the chip from it's programming station and place it in-circuit to+the chip from its programming station and place it in-circuit to
 operate. operate.
 +
 +=== Appendix ===
 +
 +Thanks must go to Tomas Lorenc who has notified me a fix is required
 +for devices which have MCLR configured as an I/O. In this situation
 +a device is not brought out of reset and into programming mode due to VDD
 +being raised first. Here he presents a fix for this situation.
 +
 +{{:projects:hi-pi-mod.png?200}}
 +
 +For example, the PIC12F675 has this feature in it's configuration word.
 +
 +<code>
 +bit5
 +MCLRE: GP3/MCLR Pin Function Select bit(5)
 +1 = GP3/MCLR pin function is MCLR
 +0 = GP3/MCLR pin function is digital I/O, MCLR internally tied to VDD
 +</code>
 +
 +