PIC16F628A Programming

Low-voltage programming requires dedicating RB4 to PGM function.
This is controlled by the LVP bit in a config register; when
LVP=1 then RB4 is unavailable, the pin becomes the PGM pin. It
is shipped this way from the factory.

Therefore, to use RB4 as a programmable I/O pin -- clearly
desirable -- high-voltage programming must be used, which overrides
this, and when programming the device the LVP bit must be written
to 0. Once this is done low-voltage programming is disabled and
RB4 is a normal I/O pin.


Programming mode is selected by raising /MCLR to high-voltage;
see the programming docs. 

Programming pin assignments, in program mode only:

PGM	RB4
CLOCK	RB6
DATA	RB7
Vpp	/MCLR

LVP	internal config bit