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[?] PIC16F628A - are all I/O ports tri-stated when chip is reset.

D

David Chapman

Jan 1, 1970
0
Greetings,

I wish to use two PIC16F628A processors in a particular circuit I'm
putting together. They will each have a different clock oscillator
frequency, and only one PIC will ever need to operate at any particular
time.

Some of the I/O lines in the circuit are common to both processors so
I'd like to ask the PIC experts in this NG if, when held in the Reset
condition, it is definite that all of the 16F628A processor's I/O lines
will be tri-stated.

I'd like to keep the Vcc supply on both devices and simply switch
between them by holding the UNwanted processor in the Reset state. Is
this approach acceptable?

Before anyone rushes to point out that this is not an elegant solution
and one single processor is the correct way to go, I have to agree but
say in my defence that since I already have code written for the 16F628A
PICs and only need a couple of these dual-processor units, any rewrite
of the code for a different device would not be cost effective.

TIA - Dave.
 
H

hamilton

Jan 1, 1970
0
Greetings,

I wish to use two PIC16F628A processors in a particular circuit I'm
putting together. They will each have a different clock oscillator
frequency, and only one PIC will ever need to operate at any particular
time.

Some of the I/O lines in the circuit are common to both processors so
I'd like to ask the PIC experts in this NG if, when held in the Reset
condition, it is definite that all of the 16F628A processor's I/O lines
will be tri-stated.

I'd like to keep the Vcc supply on both devices and simply switch
between them by holding the UNwanted processor in the Reset state. Is
this approach acceptable?

Before anyone rushes to point out that this is not an elegant solution
and one single processor is the correct way to go, I have to agree but
say in my defence that since I already have code written for the 16F628A
PICs and only need a couple of these dual-processor units, any rewrite
of the code for a different device would not be cost effective.

TIA - Dave.
The data sheet says that all I/O pins are held in tri-state during RESET.

On each pin there is a diode to Vcc and Vdd.

With one device in RESET, these diodes will be seen by the other chip.

If you not using the A/D converter, these diode should not bother
digital I/O.

Good Luck, let us know how it goes.

hamilton
 
H

hamilton

Jan 1, 1970
0
The data sheet says that all I/O pins are held in tri-state during RESET.

On each pin there is a diode to Vcc and Vdd.

With one device in RESET, these diodes will be seen by the other chip.

If you not using the A/D converter, these diode should not bother
digital I/O.

Sorry, this part only has comparator inputs.
And these inputs do have the diodes.



So
 
N

Nico Coesel

Jan 1, 1970
0
David Chapman said:
Greetings,


Before anyone rushes to point out that this is not an elegant solution
and one single processor is the correct way to go, I have to agree but
say in my defence that since I already have code written for the 16F628A
PICs and only need a couple of these dual-processor units, any rewrite
of the code for a different device would not be cost effective.

Switching to a different architecture will be more cost effective in
the long run. Using 2 (or more) PICs is the beginning of life in a
world of pain.

For starters: How do you make sure that one is completely stopped
before the other starts? How do you syncrhonise both processes?
 
D

David Chapman

Jan 1, 1970
0
Very many thanks to those who took the time and trouble to answer my
posting. Much appreciated.

ATB - Dave.
 
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