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Originally Posted by Mark McLeod
The TTL port on the CMUCAM2, both 2005 & 2006 KOP releases, works just fine. No jumper is required, but you can only have one of the three CMUCAM serial ports hooked up at any one time. Even loose wires connected to a TTL port, for example, will make that port look active and the CMUCAM2 board will get too confused to communicate properly.
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I'll admit I never tried it myself. The original CMUcam2 design included a "serial bypass" jumper which I believe was used to disconnect the RX line from the MAX232 chip (so that the MAX232 would not be driving the pin in conflict with the TTL port). I didn't see this jumper on the IFI version of the CMUcam2 so I figured it was omitted, but perhaps the RS232 chip they used tri-states without valid input. I planned on sticking with RS232 levels anyway so I didn't worry too much about it. Good to hear that it works though.
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I'll echo Dave's comments on TTL & noise, actually any PWM cable and strong electrical fields. I'd suggest using shielded cable for TTL or any communication, but in any case monitor your final solution looking for susceptibility to noise especially if the cable is routed anywhere near magnetic fields such as those around the CIMs or alongside power lines.
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As an interesting note about noise, we actually have the opposite problem on our 2006 robot: the serial communications lines are run (unshielded) right next to some PWM wires, and when the robot is disabled (which tri-states the PWM outputs) the noise from the RS232 communications causes the servos which control the tilt on our camera to twitch. It causes the case of our camera to bang into the frame of our robot and sounds like a woodpecker
. We decided it wasn't enough of an issue to justify re-running shielded wire but it gets annoying when the robot is disabled for any length of time!