Multiple download cable connection

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Vmax

Member
I’m looking into parallel processing using two PICAXE 28X1, with one as Master and the other as Slave. Both have serial download cable ports and it’s a pain switching from one port to the other to reprogram Master or Slave. I was thinking of doing something like this:

P1.JPG

Pins 14 and 15 are on an I2C bus. Slave pin 28 goes to Master input pin 18. Reset goes to pin 1 on both Master and Slave. Serial in pin 6 goes to Master and Slave, as well as serial out pin 7.

Both Master and Slave are disconnected. With a menu system, the idea is to select an option to reprogram chips, with options to reconnect either the Master or the Slave to the download cable.

I haven’t tried to download yet, because serial out using SERTXD on Master or Slave doesn’t work. There’s nothing coming out. I’m guessing there’s something wrong with the circuit between pins 6 and 7 on Master and Slave.
 
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inglewoodpete

Senior Member
Connecting the two "Serial Out" pins together without some form of protection is not a good idea. What happens if one PICAXE responds to a download request quicker than the other? One Serial Out will be high and the other will be low - a high current can flow from one chip to the other and damage them.
 
S

srnet

Senior Member
Vmax said:
because serial out using SERTXD on Master or Slave doesn’t work. There’s nothing coming out.
Click to expand...
Well you do have both serial output pins tied together.

If one serial out is in the low idle state, how can the other serial out go high to send the serial data ?

And of course there is a risk of damage to the PICAXE if two output pins are directly connected to each other.
 
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Paix

Senior Member
I don't know any of the answers, but the subject has been broached before and I'm not sure if there was some limited degree of success. One of the regular posters was responsible for bringing it up in the last six to eight months if my memory serves me.

Part of the problem is that the dialog is a two way thing, at least initially. the PC speaks to the chip and gains a response and the dowload commences. You would have two Picaxe transmitters in contention and you couldn't reliably ignore one unless you could guarantee that both chips were ready in the same window of opportunity.

how much handshaking goes on could me monitored by sniffing with LEDs the transmit and receive pins during a download, but if it isn't trivial then you are likely to be flogging a dead horse.

Others will doubtless be able to give you a bit of a more up to the minute analysis of the problems you might face.
 
Buzby

Buzby

Senior Member
It is so much easier to use use two cables and run two instances of PE.

What exactly are you trying to do ?. Same prog to many chips, or different progs to each chip ?
 
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