Two PICAXE same download circuit?

[bpowell]

Hi Gang,

I'm thinking of a design that will be able to use either a 08M2, or a 20X2...so I've designed a circuit with one download circuit which will go to both chips...so if the 8M2 is populated, it's all set...if the 20X2 is populated, it's all set.

However, I've thought there might be a time I want both chips populated...in which case...I'd put a jumper header on the SERIN line (after the 22k) to "select" either the 08M2 or the 20X2...then.

I'm thinking: When the programming is done...I'd bridge the jumper so both the 20x2 and the 08m2 are tied-low using the same 10k / 22k pair. Also, I'd leave the SEROUT connected...so, the 20X2 and the 08M2 would have their SEROUTs tied together.

Any concerns with this setup? As I type it, I'm thinking I'd like to see a 1k on one of the SEROUT lines (to prevent an accidental HIGH one one chip, and LOW on the other...maybe not "accidental" that's just serial comms...)


On the SERIN side...maybe I should just add a 22k/10k pair for both chips, and move the jumper header between the download connector and the resistor pair? That seems more sane.

Okay...so, will a 1k on the SEROUT affect serial comms / downloads? Would this be enough to allow both PICAXE to share the SEROUT?

Thanks!

 

[AllyCat]

Hi,

I'd put a jumper header on the SERIN line (after the 22k) to "select" either the 08M2 or the 20X2..

NO!, you must put the (primary) jumper to select the OUTPUT of the chip which is being programmed, because the "verification" signal sent back controls the programming.

There is possibly no harm in joining the input pins together (even with shared 10k + 22k), provided that you don't mind if the program in the "unselected" chip might get corrupted. You can never (correctly) program two PICaxes in parallel (and certainly not if they're different types! ).

Cheers, Alan.

 

[bpowell]

Got it, thanks! So there is risk in having the outputs tied together...I recognize the PC needs the output from the target picaxe before it will proceed with the programming...I will redesign accordingly.