Use of DTR in JP1.2/3 serial cable

beta2k · Post by **beta2k** » Sat Jun 13, 2009 11:39 pm

DTR in Tommy's JP1.2/3 interface goes through a 4.7k resistor to Rx/the collector of Q3. What is DTR providing? A pullup to the serial port's VCC? Or is it switched on/off as part of the communications? I use a FTDI TTL232R for a USB->Serial adapter on most things since it eliminates needing a MAX232 or similar as I normally deal in TTL levels but it doesn't bring out DTR/DSR. I have VCC available if it's just a VCC pull-up.

Thanks

Tommy Tyler · Post by **Tommy Tyler** » Sun Jun 14, 2009 11:18 am

What is DTR providing? A pullup to the serial port's VCC?

Exactly.

beta2k · Post by **beta2k** » Sun Jun 14, 2009 9:30 pm

Well I tied R3 to VCC and no love

I'm not getting any LED output from the remotes (I have a JP1.2 1055 and a JP1.3 1055) when I run jp1xtest. Starting to wonder if I need to pull RTS high as it's a open collector output it looks like. I guess I'd need to pull it high and take it through another transistor to get the right sense input to Q2 right?

Tommy Tyler · Post by **Tommy Tyler** » Mon Jun 15, 2009 5:54 am

It sounds like you are modifying the design from that in my schematic, but it's hard to tell exactly how. Unless you post a schematic of what you're trying I can't offer any advice.

Tommy