WIZ127SR for RS-485 applications

Question

We use FW Version 1.0 and the user manual version 1.11 (UM) The technical notes and the user manual claim, that the WIZ127SR is able to support RS-485 connections. The physical layer needs a driver. This is described on page 7 of the UM. To work properly, a special behavior of the RTS signal is necessary. On page 11, this is called “RTS only for RS485”. Unfortunately, this mode cannot be selected in either interface. Not in the config tool, not in the WEB interface not from within the telnet dialog. I guess, this could be easily added in the dialog. Potentially, this is not yet provided because of the behavior of the RTS signal itself. The description in the user manual is somewhat confusing. The RTS behavior for the RS-232 is described on page 36 for the “RS232 Level”. Usually, this signal is described for the TTL level, the level at the WIZ127SR pin. This is low active for RS-232. For the WIZ127SR it seems to be made inactive, if the transmit buffer becomes empty. This is so far correct. For RS-485, there is no RS-485 level for the RTS signal, this signal is not transferred over the cable. It controls the output enable of the driver and is high active. It must stay active until the last byte is completely transferred. Thus, the timing on page 38 is correct, but low and high must be interchanged. I have in my prototype the WIZ127SR with the drivers disconnected and replaced by another RS-485 converter. In seconds, I could change that back. This way, it would be nearly no work to test a new firmware version (and / or maybe a new setup tool).

ywkwon · Answer

Please download the configuration tool version 1.0.0.2. It has been updated a while ago. It can set the RTS Only mode on Flow control menu. [url]http://www.wiznet.co.kr/UpLoad_Files/ReferenceFiles/WIZ127SR_config_v1.0.0.2_install.zip[/url]

qrgc1 · Answer

Thanks for providing me with a new setup tool. The dialog allows to setup “RTS only”. Unfortunately, RTS will not work (FW 1.0). I tried to transmit single characters and observerd RTS with an oscilloscope. For UART1 RTS is held high (3.3V) and UART2 is held low, no change while transmitting the character.

ywkwon · Answer

We fixing the RTS signal bug and testing now. The new firmware will release soon.