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Bi Directional Serial Buse Problems (MORE DEAD STAMPS......) — Parallax Forums

Bi Directional Serial Buse Problems (MORE DEAD STAMPS......)

ArchiverArchiver Posts: 46,084
edited 2003-03-14 15:15 in General Discussion
Hi All,



I have built a bi directional data bus for communication between to stamps with
flow control.



The problem is that occasionally one of the stamps will die and refuse to
communicate serially any more. Nothing is shorting, each is in a nice PCB in a
simple circuit.



It looks like it's the flow control pin that is dieing in each case. What I am
wondering is whether it is possible to protect each stamp pin (flow control and
serial data) for each stamp without effecting the data. As each stamp is in a
different portable box, it is necessary to protect each stamp individually.





Can I do this...



|

BS2E FLOW PIN
RESISTOR
RESISTOR
BS2E FLOW PIN



BS2E SD I/O DATA
RESISTOR
RESISTOR
BS2E I/O DATA

|

ONE BOX |
THE OTHER BOX













I don't want to go for an optocoupler, unless it's absolutely necessary, as I
have never used one and it would require MAJOR redesign of my PCB. Besides, not
sure how u would make a bi-directional optocoupled bus.



If the resistor method works, what values should I use?



Any help appreciated,



Regards,



Dwain



[noparse][[/noparse]Non-text portions of this message have been removed]

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-03-14 13:37
    In a message dated 3/14/2003 2:30:16 AM Pacific Standard Time,
    dwainsworld@e... writes:

    > Hi All,
    >
    >
    >
    > I have built a bi directional data bus for communication between to stamps
    > with flow control.
    >
    >
    >
    > The problem is that occasionally one of the stamps will die and refuse to
    > communicate serially any more. Nothing is shorting, each is in a nice PCB
    > in a simple circuit.
    >
    >
    >
    > It looks like it's the flow control pin that is dieing in each case. What I
    > am wondering is whether it is possible to protect each stamp pin (flow
    > control and serial data) for each stamp without effecting the data. As each
    > stamp is in a different portable box, it is necessary to protect each stamp
    > individually.

    I have never done "flow control" but an easy way to isolate one stamp from
    the other is using opto-isolators. Just off the top of my bald head, I would
    think that one of the considerations is the speed at which you are sending
    data. The opto isolator can turn on then off only so fast.

    Ken


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2003-03-14 15:15
    1. When you say 'Die', is the pin bad forever?
    Or just until you cycle power?

    2. Yes, tieing two Stamp pins together can have
    the effect of tieing two drivers together, IF they
    are both Outputs at the same time. IF one tries
    to drive to 0, AND one tries to drive to +5,
    you'll have a short through the drivers (for a
    a very short time) and one
    can burn out. The simple fix for this is to
    (as you suggest) put some serial resistance in
    the line to reduce the current. Values can be
    220 to 1000 ohms, and yes, they can be spread
    across multiple boxes. You also might want to
    put the Flow pins in INPUT mode when not being
    used for a message.

    3. IF you are using SEROUT/SERIN (as you imply)
    then you can use the 'Open Collector' mode. This
    lets the 'bus' line float high (through a 10K
    resistor to +5) and only drives low, so you never
    have two drivers in opposite states.

    4. #3 does not help for the flow control pin,
    so yes, putting the separate serial resistors
    on the flow pin(s) will work. I've been told
    they may slow down transitions -- but this is
    the Stamp we're talking about, it works very
    slowly compared to wire signaling rates.

    --- In basicstamps@yahoogroups.com, "Dwain J. Hill"
    <dwainsworld@e...> wrote:
    > Hi All,
    >
    >
    >
    > I have built a bi directional data bus for communication between to
    stamps with flow control.
    >
    >
    >
    > The problem is that occasionally one of the stamps will die and
    refuse to communicate serially any more. Nothing is shorting, each is
    in a nice PCB in a simple circuit.
    >
    >
    >
    > It looks like it's the flow control pin that is dieing in each
    case. What I am wondering is whether it is possible to protect each
    stamp pin (flow control and serial data) for each stamp without
    effecting the data. As each stamp is in a different portable box, it
    is necessary to protect each stamp individually.
    >
    >
    >
    >
    >
    > Can I do this...
    >
    >
    >
    >
    |
    >
    > BS2E FLOW PIN
    RESISTOR
    RESISTOR
    BS2E FLOW PIN
    >
    >
    >
    > BS2E SD I/O DATA
    RESISTOR
    RESISTOR
    BS2E I/O DATA
    >
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