Advice required on which IC to use

Question

Hi I have just designed and produced a number of products that have been designed to take a plug in ethernet to serial pcb based on the Lantronix Xport. I am having issues with the Xport’s RTS that Lantronix have yet to provide a solution and the issue has become urgent. My requirements are quite simple. Receive commands via TCP on Ethernet and convert to asynchronous format using 8 data bits, no parity and 1 stop bit (8N1) @ 2400 baud. RTS & CTS are required. Send any data on the serial in port to ethernet (again 8N1 2400 baud). There is no control on data flow and any buffer over-run is accepted. We will have to design our own pcb as the footprint and connections are already laid down with the other pcb’s. My knowledge of Ethernet TCP-IP is limited to the Xport and comprises simply setting IP address and port. Can you please advice best chip, recommended circuitry and gui program for setting up. Mike

Hanspeter · Answer

Hi Mike, Although you did not specify the WIZ module you are using I would assume it’s a WIZ107SR. I never got the RTS pin on the hardware to respond correctly to UART data bytes exiting the WIZ107SR! The RTS pin was always logically held LOW. The ONLY time RTS pin is pulled logically HIGH is when you Hard reset the module, RTS TTL pin is briefly toggled from LOW to HIGH for ~ 440mS. I can say for certain that when you drive the CTS TTL LOW the WIZ107SR can pass incoming data from TCP/IP network to you on the UART side. My suspicion is that the W7100 chip has only 64kb code space and perhaps has been left unimplemented such as RFC2217, as there no more code room. Cheers, Hanspeter.

Hanspeter · Answer

Hi Mike, Receive commands via TCP on Ethernet and convert to asynchronous format using 8 data bits, no parity and 1 stop bit (8N1) @ 2400 baud. RTS & CTS are required. The WIZ107SR has a 2kb Tx buffer and a 2kb Rx buffer, and Wiznet design goal as I understand it in connection with RTS/CTS is: RTS is always active and will pass serial data to you on the UART side, If on the other hand your microcontroller on the serial side is NOT ready to process serial data from E2U ie (Ethernet-2-UART), just deactivate CTS line on WIZ107SR pin and any incoming data on the Ethernet side will be buffered till you signal on the CTS line that you are ready to receive your data. You must be mindful of WIZ107SR 2kb Rx buffer! else you are going to lose incoming data on the E2U side of the link ie buffer over run. As far as I have tested, RTS pin is always in active state to you indicating E2U data will be passed on to you on the UART end as long as you hold the CTS pin High, and if your WIZ107SR is TTL version CTS must be Low. Cheers Hanspeter