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Connecting Two Stamps

ScottishCaptainScottishCaptain Posts: 10
edited 2006-04-08 17:32 in BASIC Stamp
Greetings to all!

I've got a quick question about connecting two Stamps together.

One is a BS2SX, the other is a Javelin.

I plan on using SERIN and SEROUT to communicate between the units.

My question is this. The pins I'm using are part of a PCB that primarily wasn't intended to be used for communication between stamps.
Each of the 5 pins I need to use have a LED and a 1kOhm resistor hanging off to ground (should pull about 5mA).

So, what are the source current limits for the Stamp units when using RS232 TTL (SERIN/SEROUT)?

Is it the same as if you were driving the pins High/Low manually (30mA/Pin, 60mA Total for the entire unit)? Or is it something else?

Cheers!

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-07 23:39
    Hello,

    ·· First of all RS-232 and TTL are totally different signal levels.· You will be dealing with TTL, not RS-232, and experience has shown me that the LEDs don't usually cause much of a problem, although the baud mode you choose (inverted or true) will determine if the LEDs are on all the time but pulse off during activity or if they're off except pulsing during activity.· Think of them as little activity indicators.· I only say this because it's already there.· I don't normally recommend wiring things like this.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • ScottishCaptainScottishCaptain Posts: 10
    edited 2006-04-08 05:41
    Yes, sorry... You are correct. I'm still new to Parallax's micro controllers. It is indeed TTL.

    The baud mode will most likely be 9600, non-inverted.

    Just curious- why don't you recommend wiring them like this? Is there a particular reason (Aside from the obvious fact of needing the LED's), or could there be some sort of long-term effect on the controllers?

    If need be, I can replace the LED's with wire, just leaving the resistors. I can also replace the 1KOhm units with 10KOhm or larger. I just figured that since they come with the kit, might as well use 'em.

    Thanks!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-08 17:32
    As I was saying it shouldn't cause a problem.· Usually you would use a driver to monitor the signal line.· But on occasion I have myself tied an LED from the serial signal line to Vdd, that way each bit flickers it on.· Just keep the line lengths short a low current on the LED if you're going to do this.· Sounds like your circuit should work if you're not running long wires between the two devices.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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