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No. 1177	Re: Problem connecting CSW-M85 to existing design	2013-04-15

Dear Jonas Larby Yes, there's 10K pull-up resistor on the serial TX line of CSW-M85. It is pulled up by AR1 in the bottom. I am afraid but it can't be disabled by software. The only way to disable it is removing AR1 (4 array resistor) in the bottom. The RXD1, TXD1, CTS1, RTS1 are pulled up by this resistor. Best Regards, Matthew Lee > Jonas Larby wrote: > ------------------------------------ > Hello! > > I am trying to use CSW-M85 to an existing system. Everything works fine when I use your Evaluation Board, but I got problem when connecting directly to the module using TTL 3.3V levels. > > I get data out of CSW-M85, but can't sink data zeroes to CSW-M85 enough to be a valid zero. I think that your module has an internal pull up of about 10K. My existing system has a serial resistance at TX of the same magnitude explaining the problem... > > Is there any way to disable the internal pull up of CSW-M85? > > Grateful for any hints! > > Best regards, > > Jonas Larby. > > MSc/Software Consultant.