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RS232 debug on JS16

Question asked by ROB LUND on Jul 31, 2010
Latest reply on Aug 2, 2010 by ROB LUND

(Ugg, how embarrassing is this, right?)

So I'm getting the SCI port on my JS16 DEMO board off its feet.  This board has no RS232 transceiver on it, so I've got my own little add-on board with an ICL3232 and serial DB9 cable.  This cable has been proven to work with other UART projects.

I've got the SCI port enabled and transmitting, as I can verify with an o-scope on the transmit pin.  Nice strong +5V inactive, driven to ground when active.

When I plug in this transceiver, the transmit line gets loaded down and my JS16 can't drive all the way to ground (only about a volt).

Looking at just the transceiver, with its TTL TX and RX shorted together in loopback mode, I can transmit and see echo on a PC serial monitor.  So I know that the chip is alive and working independently of the JS16.

Why don't they work together?  I've checked pinouts and power and port pins twice over.