Pullup resistor requirements

[alhoop]

All my Picaxe 08 and 20M chips require a pullup resistor on the pin
assigned to serout. My lone 14M does not. Is this normal?
Thanks
Al

 

[westaust55]

No this is not normal for direct connection to the PICAXE pin.

Are you wired through a ULN2803 or similar Darlington Transistor ? These a basically open collector and can only pull the signal low (they float when the signal is hig) thus will require a pull-up resistor.

If not due to Darlington transistor, please post your circuit(s) so that we can review further.

 

[alhoop]

Thanks for the response.
No circuit other than the serial download and power. +5v from a Heathkit trainer through a 1N4004.
Serout to physical pins - 6(logical 1) on the 08, 8(logical 5) on the 14M and 11(logical7) on the 20M.
No activity on the 08 and 20M without a 4.7k pullup resistor,
serial activity on the 14M with no pullup. I know I could not find any
info on this in the manual although I am not familiar with everything there.
Al

 

[westaust55]

Strange (unless I am missing something), do you have the same problem say with the 08(M) if you use output2 instead of output1 ?

 

[alhoop]

Looks like I cried wolf for no reason - an 08,08M, 14M and two 20Ms are now working properly with no pullup. One basic 08 works off and on with no pullup.
Sorry
Al

PS No chip problems, my new DSO Nano oscope has an intermittent probe, the one with a unique connector.

Thanks Westy!!