> I have a circuit with a pic16c74 (may become a 16f74 later or 16f874)
> connected to a 6264 ram chip, with rb6 and rb7 being used as output pins
> connected to two of the 6264's address input pins. What 'isolation
circuit'
> (Microchip's term from spec TB013) should i use on these lines if i am
> attempting to use ICSP?

As only the PIC drives these lines: nothing. The R's are needed when the
rest of the circuit could drive the lines, which would give problems with
the ICSP use.

> Also, what about the mclr pin? I was planning to use an IN4148 diode and a
> 10k resistor but do i need a pull down capacitor as well?

For ICSP MCLR must be brought quickly to around 14V. So there are a number
of reset 'circuits' that will work. The most simple 10 - 40 k to Vcc, but
that might not work unless at least the chip has brownout detection. An
external brownout detector must not be connected directly to MCLR, but
rather 'halfway' into the R. Many other options are possible. Remember that
a C directly on MCLR is taboo, even more so for ICSP.

> And finally... on the same spec TB013, the Vdd of the pic is connected to
> the Vdd line via a resistor; what value is sensible?

Probably to prevent problems when power of circuit and programmer are
slightly different?

Wouter van Ooijen

Van Ooijen Technische Informatica: http://www.voti.nl
Jal compiler for PIC uC's:  http://www.voti.nl/jal
PICs kopen? http://www.voti.nl/shop

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