clarifcations in circuit setup for 16f8x icsp programming ??

[spyghost]

hi,

i have read the icsp guide in the microchip website (https://www.electro-tech-online.com/custompdfs/2004/05/30277d-3.pdf)

i focused on the 16f8x programming. there is a circuit at the bottom of page 2-21 (figure 1: typical application circuit). i am very noob in icsp/isp and i would like to learn using it... i have several questions that really need clarification:

- is the diode found in mclr/vpp already enough?
- can a simple tri state buffer be used as an isolation for rb7 and rb6? i found this (https://www.electro-tech-online.com/custompdfs/2004/05/sn74lvc2g240-3.pdf)
- if i use tri-states, is there a way to automatically switch the gates to its its hi-z state during programming? or i simply need to place jumpers/dip switches to make it hi-z?

if there is further information that may be useful, plese feel free to add...

thanks!

 

[Exo]

Re: clarifcations in circuit setup for 16f8x icsp programmin

hi,

i have read the icsp guide in the microchip website (https://www.electro-tech-online.com/custompdfs/2004/05/30277d-4.pdf)

i focused on the 16f8x programming. there is a circuit at the bottom of page 2-21 (figure 1: typical application circuit). i am very noob in icsp/isp and i would like to learn using it... i have several questions that really need clarification:

- is the diode found in mclr/vpp already enough?

Yes, The 14 volt programming voltage will reach the chip directly while the diode prevents the 14V from getting to the power rail.

- can a simple tri state buffer be used as an isolation for rb7 and rb6? i found this (https://www.electro-tech-online.com/custompdfs/2004/05/sn74lvc2g240-4.pdf)

If you put it to H-zi when the circuit is operating it shouldnt interfere, I think it should work. On the other hand why not connect RB6 - RB7 to something that won't react when the device is powered off. For example, if you use RB6 - RB7 to drive leds and those leds are not powered during programming, then they won't react to programming signals.

- if i use tri-states, is there a way to automatically switch the gates to its its hi-z state during programming? or i simply need to place jumpers/dip switches to make it hi-z?

You could modify your ICSP plug to have an extra pin, wich for example, provides a 5V signal. You could then use this pin to switch the tri-state. Plug the programmer on the board, power it on and the tri-state will switch automatically. I use the same system.

if there is further information that may be useful, plese feel free to add...

I would replace the resistor between VDD and the pic with a diode. The resistor thing will work, but only if nothing draws a load from your pic. If you , for example, drive 5 leds of your pic, then the current used by these leds eventually come from the VDD line, the current required will generate a voltage drop across the resistor. It will quickly become to high and the pic will shut down.

 

[spyghost]

speaking of isolation, i was just puzzled by this circuit:
(**broken link removed**)

is this circuit good enough for icsp?

 

[Exo]

That's basically the same as the circuit in microchip's App note. though, the VDD system is better, using a diode in stead of a resistor, like i said

 

[spyghost]

what about the resistors found in the rb6 and rb7?

 

[Exo]

Like i explained in the previous post, if you use these 2 pins to drive something, a transistor perhaps, then it will work fine, the 2 10K resistors work nice as base-current limiting resistors, and because the rest of the application should be turned off while programming there isn't anything that will respond to the programming signals.

If you want full I/O functionality from those pins it would be better to add some kind of isolation, such as your tri-state for example