Hydra as a Propeller programmer ... not?

Jasper_M

The USB2SER input on Hydra, intended for programming hydra with an external programmer, works also as an output.

You just have to connect the USB2SER pins to the Propeller <EDIT>P31 & P30 through resistors, 330ohm-1Kohm should be fine, according to Mike Green</EDIT>, from left to right 1. /RESET 2. P31 3. P30 4. GND

Hydra has to be powered during programming (resulting in the Hydra being programmed as a side-effect). But it doesn't matter even if two Props are programmed simultaneously. The output signals from Propellers don't interfere with eachother : )

For some reason, I fried a prop once again. With some 500ohm resistors. And power supply @ 3V3 current-limited to under 20mA. I've got no idea what's going on but you shouldn't prolly use this -.-'

Post Edited (Jasper_M) : 4/16/2008 4:52:56 PM GMT

Mike Green

That's not quite true. P30 is used as a transmit (output) line and when you connect two outputs together, you can damage one or both of them from the short circuit that occurs when one output is in the high state and the other is in the low state. At the very least, you need a current limiting resistor between each P30 and the common USB2SER connection. Any value from around 330 Ohms to around 1K should work ok. The two P30 pins should be mostly in the same state, but there'll be short periods where they may be in opposite states and damage can occur quickly. Propeller testing (for the datasheet) has shown that the output stages seem to withstand shorts without damage, but it's not guaranteed.

Jasper_M

Quite true. Also, both props get programmed with the same program and start running it. After that, the props will probably be in a different state and if P30/31 are used as outputs, it's likely that shorts will happen in that case.