View Full Version : serial communication question

01-24-2009, 12:38 AM
I am bringing an old Heathkit Hero-1 robot back to life with a propeller usb proto board. My question concerns the usb connection that uses i/o pins 30 & 31. After bootup and program download I wish to use these pins to communicate with a host. I've been doing this with the USB connection in order to debug my program but now I wish to employ my wireless serial 900MHZ spread spectrum interface that utilizes a stand DB25 serial interface. So here's my question (finally). Has anyone connected pins 30 & 31 to a Max232 interface. In other words, can pins 30 & 31 drive both the usb serial·interface ·and a Max 232 chip for host communication so long as both are not active simultaneously? If not, I'll be forced to use my remaining two I/O pinsfor wireless communication.



Mike Green
01-24-2009, 12:47 AM
You will need some kind of external circuitry to disconnect the USB interface and connect the wireless interface. There's no real problem in transmitting from the Propeller to both the USB interface and the wireless transmitter, but you can't just connect two receivers to the same Propeller I/O pin. At the very least, you'll need an OR gate (since serial communications idles at logic high (1)). That won't work though if you can't guarantee that the USB interface (and the wireless interface) idle at logic high when the USB connection is disconnected and the wireless link is off. In the end, you'll probably have to use a Propeller I/O pin to select which input to use and you might as well connect the wireless receiver to its own I/O pin.