MicroSquirt.com read only forum (Jan.15,2018)

nemiro wrote:It could be, but also check which USB-> serial cable you are using. I have found on another uS that it was VERY picky about what cable I needed to use. I ended up having to spring for the high dollar cable, and everything worked fine.

I have been digging into this a bit, and what I am discovering is that there are some cables that are not RS-232 compliant. What this means is that the voltage swing is not +/-10V but much, much smaller. I know that the MAX3221 device needs to operate within a +/- 2.5V swing range - it needs to see this level on the receive side (i.e. from PC to uS), otherwise it will go into auto-shutdown mode on the transmit side (from uS to PC).

From the Maxim datasheet:

Autoshutdown works by monitoring the RS-232 side of the receivers. When connected to another RS-232 device, the receivers will see valid RS-232 signals that are either below -3V or above +3V. On the other hand, if nothing is connected, the receivers will typically be at ground. If the Autoshutdown feature detects that all the receivers are between -.3V and +.3V for greater than 30µS, it assumes that a valid transmitter is not connected and will automatically put itself into a low-power mode. The part will automatically take itself out of the low-power mode if any one of the receivers' inputs exceeds +2.7V or goes below -2.7V.

So - your computer needs to be supplying a valid RS-232 level. I know that the USB-to-Serial cable I use has a "Prolific" chipset and it provides RS-232 signalling (I scoped this myself). The one I have is the brand name of Sewell and can be purchased for $12.00 online from several sources.

- Bruce

Thanks to all of you out there for your inputs.I tried replacing the db9 connector but after further investigation,I am quite convinced the uS is pooped.I am getting 5v on the bootloader wire but the download v2.0 seems to upload code and verify without the bootloader wire grounded.I think I may have a prolapsed processor from what I have read on the forum (Jankos may '09).Now I definately need assistance from the world outside my shed.