Problems booting BS2SX with 3 serial IO's connected

JohnSchwab

HI,
I'm hoping you can help me. I have a BS2SX with 3 serial ports
configured to communicate with some little motion controllers that
take commands via serial communications.

The problem is that when I have more of these serial devices than
one attached, and it doesn't matter which ones, the BS2SX will not
power up.

But if I only connect 1 device, the BS2SX powers up just fine. Then
I can reconnect all the others, and trip the reset on the BS2SX and
it boots up fine. But with more than 1 serial device connected, the
BS2SX won't power up from a cold power up.

Any ideas about what is keeping it from booting, and how to fix it?

Thanks,
/John

Post Edited By Moderator (IT Guy) : 7/27/2004 3:00:05 PM GMT

Stephen Swanson (Parallax)

Hello,
Are you able to program the stamp with the 3 serial lines attached?
If so put a debug statement at the top of your code like debug “hello” and reprogram the stamp. After the stamp is programmed leave the debug window open and power down and power up the stamp. You should see the debug display the hello again. If it does then the stamp is running and the error might be in you code. If it does not display “hello” then there might be a power problem and check the VDD pin to see what the stamp is at.

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"The more you do, the more you know"

Jon Williams

Are you powering these devices from the BASIC Stamp's Vdd pin? Maybe this is the problem -- the BASIC Stamp's Vdd pin can only supply about 50 mA. Perhaps one of these devices doesn't provide enough load to affect the BASIC Stamp, but three is just to much. I would suggest a beefier power supply -- don't use the BASIC Stamp's Vdd pin to provide power to your motion control devices.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

JohnSchwab

Thanks for the guidance that put me on the right track.· I found the problem, and am working on a solution.· The problem is that the receive line of the serial port on·the motion controller is low impedance (1.1K Ohm compared to 18M Ohm on my PC serial port).· The stamp can handle one of those connected, but not three and boot up.· Once booted, the loads are not a problem for the stamp.·Whoever heard of a serial port pulling a real load anyway?· I'm working on some simple circuitry to reduce the load of the serial ports, or disconnect them with a transistor until after bootup.