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Serial comunication loop back echo? Does the Propeller have this feature? — Parallax Forums

Serial comunication loop back echo? Does the Propeller have this feature?

RonPRonP Posts: 384
edited 2011-01-19 11:02 in Propeller 1
Hello All,

I have searched and searched for this answer sorry if its right in front of me, and I can't see it.

Loop back echo. Does the Prop have this feature?

I read about the Stamps having this feature.

Thanks,

Ron

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-01-19 10:23
    No, it does not have this capability built-in. It can be programmed to do an echo while a user's code is running, but it would not respond this way during the reset/bootload interval. One work-around would be to put about a 2.2K resistor between pins A30 and A31, which would provide the echo until A30 is driven from a program.

    -Phil
  • RonPRonP Posts: 384
    edited 2011-01-19 10:26
    Wow super fast response. Not stuck wondering now I'll move on.

    Thanks Phil

    Ron
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-19 10:31
    Loopback is simply a result of the DSR and RTS control lines (on the DB9 serial connector) being connected together on the Board of Education. This was done to give some indication of whether the serial cable was plugged in. Echo is an artifact of the RS232 to logic level circuitry on the Stamp. The output circuitry (to the PC) borrows the negative idle voltage of the input circuitry to the Stamp (from the PC) in order to generate the idle voltage of the output. This is normally around -5V.

    The Propeller normally uses a USB to serial adapter (PropClip or PropPlug or equivalent) that doesn't need either feature. There is a 3 transistor serial to Propeller adapter circuit shown on the Propeller Downloads webpage. This "borrows" the -5V idle voltage of the receive line like the Stamp circuitry and does echo anything received from the PC back to the PC just like the Stamp circuit.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-01-19 10:40
    Ron, Mike is right of course. I forgot about the side-effects from the three-transistor circuit, which is still used in some Propeller designs.

    -Phil
  • RonPRonP Posts: 384
    edited 2011-01-19 10:46
    Mike thanks for the explanation. You know 6 months ago I wouldn't have understood a word you just said. So I must be learning something, cause it actually makes some sense to me. :smile:

    Now I am going to try and find out how the Prop Tool, BST or any other program for that matter figures out there is a Prop. Hints welcome.

    -Ron
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-19 10:57
    The Prop Tool and BST talk to the Prop and the Prop talks back. This PropellerLoader Spin program shows what gets sent back and forth.
  • RonPRonP Posts: 384
    edited 2011-01-19 11:02
    Thanks Mike, and its not all in PASM. I can actually understand most of it.

    -Ron
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