(+ve supply): if the target PIC operates at other than +5 volts then this pin and the MCLR/Vpp, RB6
and RB7 programming pins must be totally isolated from the target during programming.
If the target operates at +5 volts and a PICSTART+ programmer is used then the target PIC may be left
connected to the target circuitry. If however the target loads the 5 volt ICSP supply by more than a few mA
then it will not be possible to perform ICSP. In such cases programming may be possible by powering the
target from its normal +5 volt supply during programming but this is
not
recommended.
If the target operates at +5 volts and a programmer is used which checks for correct programming at other
than 5 volts (a PROMATE for instance) then this pin and the MCLR/Vpp, RB6 and RB7 programming pins
must be totally isolated from the target during programming.
RB6, RB7:
the loading of these pins by the application circuit must be zero or low. Ideally the pins should
be open circuit and often this can be accomplished by using the pins as switch inputs with internal pull-
ups. (assuming normally open switches)
MCLR/Vpp:
this pin is pulled to +13 volts during programming and must be isolated from the rest of the
circuit during programming.
Where the pin is simply pulled high to Vdd, a simple solution is to use a resistor of say 47K between the
pin and the Vdd rail. This will clamp the reset line during normal running but allow the ICSP signal to pull
the pin to the programming voltage and without damaging other circuitry on the target board. A better
solution is to use a Schottky diode to connect the pin directly to the Vdd rail with the cathode connected to
MCLR/Vpp pin of the PIC.
Where an external RC reset circuit is employed then it will be necessary to introduce a Schottky diode
between the pin and the RC reset ‘point’. (cathode connected to PIC)
Programmer types and target circuit
When using any ICSP adaptor, selection of the device programmer and the configuration of the target
circuitry is critical if successful programming is to be achieved. At worst, it may be possible to damage
both the target and the programmer if care is not taken. The problem arises from the fact that after
programming is complete, many programmers check the device at voltages other than 5 volts and if the
device is connected in the target to a fixed 5 volt supply then this may cause incorrect measurements to
be taken or in extreme cases, device and programmer damage. In these cases the user must ensure that
the target PIC pins Vdd, Vpp, RB6 and RB7 are completely isolated from the target application during
programming.
Note that the PICSTART Plus development programmer checks for correct programming at +5 volts only
and that in most applications running on a 5 volt supply this limitation does not apply.
Disclaimer
Information given in these instructions is intended for guidance only and no liability is accepted for any
loss or damage which may be caused either by use of the adaptor or by errors or omissions in these
instructions. No representation or warranty is given. Use of R.F.Solutions as critical components in life
support systems is not authorised except with express written approval from R.F.Solutions Ltd.
R. F. Solutions Ltd.,
Lewes, England
Tel +44 (0)1273 898 000
Fax +44 (0)1273 480 661
www.rfsolutions.co.uk
Email sales@rfsolutions.co.uk
R F Solutions is a member of the Low Power Radio Association.
Information contained in this document is believed to be accurate, however no representation or warranty is given and no liability is assumed by R.F. Solutions Ltd. with respect to the accuracy of
such information. Use of R.F.Solutions as critical components in life support systems is not authorised except with express written approval from R.F.Solutions Ltd.
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