8M power-up problem

[harolds1956]

Hi, I'm using an 8M and noticed output 0 goes high and low in a pattern then the program runs fine. I'm assuming it's the 8M trying to read a new program @ start-up. My project needs 3 analog inputs with 1 output so I'm forced to use 0 as an output. Is there a way to prevent this series of "on-off" when power is applied?

 

[inglewoodpete]

Harold, basically no.

Like most comms arrangements, the PICAXE needs 2 active leads for programming: the download data from the PC and the acknowledge data from the the PICAXE. In reality the return leg (Pin 0) does much more than this but basically it is an essential handshake.

Where unwanted interaction occurs, the most common solution is to include some sort of switch to the affected part (motor, led, relay etc). This can be as basic as a removable link (eg 0.1" matrix pins and jumper link similar to those used in many PCs).

 

[SD2100]

You should be able to use output 0 without any problems at startup if your code is ok and the download resistors are connected properly. Are you using DEBUG or SERTXD at the start of the program ???.

 

[Technical]

This does sound like you are missing the resistors on the serin pin... see the minimum operating circuit in part 1 of the manual.

 

[harolds1956]

Okay, here is a little more detail on my circuit. I use the recommended circuit for programming, then remove the chip from my programming board and place in my circuit. In my circuit output 0 goes to the gate of a mosfet loaded by a 10k resister. The serial in pin (and input 3) is left floating. Should I use a 10k or so pull down on serial in (and input 3)?

 

[BeanieBots]

Yes, serin MUST be held low. A 10k would be fine but for the sake of another resistor and socket, you could have the ability to program in-circuit.

It is also "good practice" but not essential to pull down any unused inputs. It will save power if you do.

 

[harolds1956]

I installed the 10k pull down on the serial in and now it works like a charm. Thanks!