Floating outputs

[steirny]

I'm sure this has been discussed before. A search reveals plenty on inputs.

Please correct me if I'm wrong, but I believe that when a picaxe chip is reset or a download initiated, then the outputs are floating.

I aim to reset some 18X's and some 08M's, (the latter by taking serial in high), using a watchdog timer. My concern is that the floating outputs may cause the motor drive bridges to behave erratically.

If I keep the reset pulse narrow, how long after release do the outputs go low? My motors may be too sluggish to respond, so no problem.

I'm thinking I should put pulldown resistors on all the bridge inputs.

Does anybody have any experience or suggestions. I have not had a chance to prototype it yet. Just toying with ideas.

 

[hippy]

It's a good question. The outputs probably go to a floating state while held in reset and are then configured output low some time after that. I would expect immediately after reset ( and held output low through download ) until the program runs.

For 08's and 08M's there is only one fixed output, so all but that would go to an input / floating output state at reset and stay that way ( through download ) until the program does run and sets the pins to outputs, so pull-ups or pull-downs could be needed there. Resetting via Serial In isn't a true reset so I don't know what would happen there.

Technical will have to provide a definitive answer.

 

[steirny]

poking serial out

Thanks Hippy

I'm using an 18X to do serial in and all 8 outputs are committed. I need to use serial out as a 9th output.

I intend to set my watchdog timer by poking the serial out high just prior to a serial in. Then reset it by a low after serial in is successful.

There was a poke to do this, but dammed if I can find it.

While on the subject of pokes. Does anyone have a list of useful and reliable pokes that could be located in the finished projects section? All the tinkerers could add to it, once proven reliable.

 

[BeanieBots]

During power up, the outputs are tri-state for 76mS.
That's quite a long time if you have critical circuitry, so pull up/down resistors are advised in such cases.

I too would welcome a "useful" pokes list.

 

[Dippy]

i thought someone did that ages ago? I'll have a (very) quick search ... yes I can search.

Maybe someone with some spare time could go through the Data Sheets and look 'em up. I'm too busy drinking coffee.

In the days before Stan changed his name there was this:
http://www.picaxeforum.co.uk/showthread.php?t=2233&highlight=underclock

All this sort of stuff can be read from Data Sheet if bothered. But a POKE list and example code (and warnings) would be a great idea.

 

[steirny]

Nine outputs on 18X

Thanks gents.

76 mS is a long time. Looks like pull downs are required.

I did a proper search and thanks to several contributors, the consensus is

POKE $05,%00000000 ' Set SERTXD line low
POKE $05,%00001000 ' Set SERTXD line high

One down, how many to go?

 

[hippy]

I've added a thread on "PICAXE SFR Usage 101" ...

http://www.picaxeforum.co.uk/showthread.php?t=8954

I put that under "Finished Projects - Communications", same place as I put the I/O pin definitions on the grounds that poking SFR's usually involved in some sort of comms programming. Couldn't think of anywhere else which was any more appropriate and at least it's a not too-busy forum which keeps it up near the top.

I added place holders for the commonest PICAXE's but need to hunt down the SFR addresses that have been identified and update them. Seemed better to do that and keep them at the top than add them in after anyone adds anything to the thread. This is a sort of one-man DIY Wiki

 

[Dippy]

Well done.