question about parallel programming

mobile_bob

the project i am working on will use
one bs2 as a master and six bs2's as slaves

further i need to parallel all the db9's together

so the question is

can i program each seperately if the power is off all but the one i want to program?

so basically power up one, program, and then power off
power up the next, program and then power off.. etc.

will there be an issue?

thanks
bob g

Mike Green

The Stamps are not designed to allow the DB9s to be paralleled together whether or not the power is on.
If you look at the circuitry from the Stamp to the PC (Sout) in the back of the PBasic manual, you'll see that
there's a PNP transistor that will function (when the power is off) as a partial short on the Stamp Sout that's
powered up.

Even if that were not the case, the Stamp's programming input circuitry uses the PC's transmit output to
supply the reference voltage for the Stamp's transmit signal to the PC. Paralleling 7 of these would load down
the signal from the PC to where it might not function properly. Similarly, the ATN inputs of the Stamps would
load down the DTR output of the PC.

You should figure on having to switch the DB9 connection. There are only 3 signals that need to be switched.

mobile_bob

ok fair enough

my next question is can the processors once programmed operate with the db9's parallel connected

or in other words will there be problems in operation if the lines are parallel connected if they are programmed

separetely?

thanks

bob g

metron9

Perhaps you should detail what task you are trying to accomplish, a different connection approach may likely come to light.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Mike Green

I don't believe you will damage anything if you leave the DB9 connectors in parallel, but I don't think you can use the serial port for programming or for anything else because of the loading on the Sin and Sout pins and likely on the capacitor networks between the DTR signal and the Atn pins.

---

I am curious why you would still want to leave these connected in parallel even if you can't program them that way.

Post Edited (Mike Green) : 5/8/2007 3:48:13 AM GMT

mobile_bob

if i cannot program them this way, i likely will not have them connected in parallel, but thought i would ask if

there would be a problem in doing so, sort of keeping my options open sort of thing.

thanks guys

bob g

Tracy Allen

I'm not convinced that it won't work. If you have the Stamps there, I would suggest you try it and let us know the outcome.

For programming, I thing a reasonably strong PC serial port could probably drive all of the ATN and TXD inputs to the Stamp in parallel. Each TXD input and each ATN input is basically 10k ohms input impedance, so 7 in parallel would still be greater than 1 kohm. For those inputs, it would not change anything for the power on 6 of the 7 to be off. Same input impedance into the bases of the NPN transistors whether they are on or off. The circuit on the Stamp that hooks TXD to RXD via a 4.7kohm resistor does not get in the way, because there is a reverse biased PNP transistor junction blocking any current flow. The more questionable thing would be, can the one Stamp that is powered up talk back to the PC by putting the handshake signals back onto the RXD line? It has to drive the seven 4.7k ohm resistors in parallel. That is about 670 ohms. Probably no problem there. Are there any diodes that would clamp the level? Not really. The diodes that might get in the way are all in the parallel PNP transistors, so they are all reverse biased. So, I say, it might work. But you have to be the one to try it!

Now, if all of them are powered up and you want one to be the master, I know that works with at least 4 in parallel, because I've used that arrangement in a token passing scheme, where a PC was master listening to all 4 as they passed the token around.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

mobile_bob

well i suppose that if it won't damage anything in trying the parallel connection
i will give it·a whirl and see what happens.

it maybe a month or so before i get to that stage, but will report back how it all works out

thank you

bob g

allanlane5

Note that using the "open" mode of the SERIN/SEROUT commands, you can easily "Party Line" network multiple BS2's together.