Prop Stick USB issue

T Chap

Hello all
I have been experimenting with a Prop Stick USB for the first time. The project is running off a 12v car battery, and uses a 5v switching regulator to power the PCB and Prop Stick. RESn is floating on the device, VDD off the device is powering an external eeprom only. VIN is the 5 volts from the external regulator(on the PCB). All grounds are tied together on the PCB>Prop Stick.

If the USB cable is plugged into a computer to the Prop Stick, the device boots normally. If the usb cable is unplugged, device runs the first set if init codes ( not all ) and reboots over and over again. I will do further testing this afternoon, but it seems like it reboots at the StartSerial method which sets up the 4 port full duplex object.

I am at a loss for this issue, if anyone has a suggestion I would be glad to hear some input.

Thanks

Mike Green

This is a known issue with most USB interfaces for the Propeller. It happens when your program tries to use the USB serial port without an active USB cable plugged in. What happens is that you're trying to transmit to the USB chip and that supplies a 3.3V signal to the chip. When there's no USB power provided (like when there's no cable plugged in), this 3.3V signal supplies enough power to the chip for it to partially activate and it works enough to produce a reset signal for the Propeller. The answer is to check INA[ 31 ] before initializing the serial port. If INA[ 31 ] is high (1), the USB port is probably active and you can initialize your serial driver. If INA[ 31 ] is low (0), the USB port is probably not powered and you should not try to use it.

T Chap

Many thanks Mike. For this new concept with the Prop stick, I had it sending out some data for debugging to the PC terminal with the 4 port. I just disabled the USB RX/TX over 31/30 and now it is working fine.

Much appreciated!