Resetting a slave from master mcu

[Demon]

I ended up with this design, using tri-state pin on master to reset all the slaves when required. This will not be used for programming the slaves, only resets.




It's simple, uses a single general I/O pin on master, and no extra components on slaves.

I include that 100R res on slaves "just in case" I need them one day with my Pik-Kit.


EDIT: For those that want to ICSP as well, look at the SN7407, and thank Mr E for the info (master on Input A, slave on Output Y)

[Ioannis]

What drives the MCLR pin of the slaves? A PIC output?

I am asking, because the MCLR pin needs a level of 0,2*Vdd to see LOW (for the 16F177x series, but I guess it is the same for others).

It depends on output characteristics if you are within limits of the MCLR. So be sure that what you think as low is actually sensed as low on the MCLR pins.

Ioannis

[amgen]

you could do in software..... send out to one or all listeners a command to goto a restart routine like.... which "provides a way to execute a MCLR in software"
,
,
,
restarting:
@ RESET

[Demon]

you could do in software..... send out to one or all listeners a command to goto a restart routine like.... which "provides a way to execute a MCLR in software"
,
,
,
restarting:
@ RESET

But will that work if the slave is caught in a loop or some such?

I'm aiming for a complete reset with no decision from the slave.

[amgen]

But will that work if the slave is caught in a loop or some such?

I'm aiming for a complete reset with no decision from the slave.

could do.........
1)
'
restarting:
pause 1000 ............... wait a second or 2 to reset all
@ RESET
'
or 2)................
if all slaves are on same 5 or 3 volt supply, then use a small NC (normally closed) relay to turn off power for few seconds to restart all slaves

[Demon]

I figured out an easier way to MCLR a PIC from another; a simple diode.




I was fixated on that darn pull-up to VDD:

- pull-down MCLR on Slave.
- 1N4001 diode from GP pin on Master.
- 100R towards ICSP.

And that's it. I just tested it, and there's never more than 5V on Master-side of diode.

I can't believe it was so simple.


I have one last test to do; check how much current is running from Master.

EDIT: I see a quick pulse of 16-17mA when I'm programming via ICSP. I'm not sure how I can manage that.

[amgen]

MCLR's have internal weak pullups in chip.....

[Demon]

could do.........
1)
'
restarting:
pause 1000 ............... wait a second or 2 to reset all
@ RESET
'
or 2)................
if all slaves are on same 5 or 3 volt supply, then use a small NC (normally closed) relay to turn off power for few seconds to restart all slaves

What is the @ RESET command? (I'm using PBP3.1)

I prefer to avoid relays and mechanical devices. Contacts generally consume more current than ICs and discretes, and contacts wear out.

I've got an order for some SN7407N from Digikey; gonna check out Mr E's suggestion.

[amgen]

diodes can be like signal diodes 1N4148. Not backwards in order to pull MCLR low to reset and that is considering you do LOW VOLTAGE PROGRAMMING setting, if not doing that then would use the 2n3906 or any NPN to pull down all the slaves through the diodes. The @ RESET is an assembly instruction using the @ for PBP to do machine code directly ( I think you know all that stuff)...... so if you want a hard reset after ICSP then yes to use MCLR but if chips are running, you could give instruction to GOTO reset.

[Demon]

What drives the MCLR pin of the slaves? A PIC output? ...

A tri-state general I/O pin on the master.

Output low = reset
Input = do nothing

...

I am asking, because the MCLR pin needs a level of 0,2*Vdd to see LOW (for the 16F177x series, but I guess it is the same for others).

It depends on output characteristics if you are within limits of the MCLR. So be sure that what you think as low is actually sensed as low on the MCLR pins.

Ioannis

I can't say. This is all theory for now, but is supported by posts on google and a forum elder, Mr E.

So I blame him if my house burns down.