Hi, my Name is Alfred, working for a small Company south of munich.

I have to make a Migration from W3100A to W3150A+.

my question:

If i set a socket do UDP, when is ist possible to read or write TX_WR register ?

always ?

after “open” command ?

I always get “0” if i read the TX_WR reg. also if i wrote some value to it ( reading is working, i can write / read all other registers).

another socket is set to “TCP”, i can write / read the TX_WR pointer of this socket, it works.

I am confused about that, tryed it for a whole day now to fix it.

Can you please help me ?

Many thanks.

Best regards: Alfred.


Sn_TX_WR is initialized by OPEN command, Thus you can read after OPEN command.
You’re now saying that the TX_WR register can not be read in UDP mode. Does it work well on the W3100A in same environment?


hello, alfred

Of Course, HOST must open socket to r/w TX_WR.

Have you ever sent data with UDP socket?

TX_WR is Socket TX Buffer Write Pointer.

It is the register written by HOST. And the register value is updated by SEND Command.

So, when HOST copy the data into TX buffer to send data, HOST must increase TX_WR as much as Data length.

Then do SEND command.

After you got 0x00 from Sn_CR, you can check the TX_WR value is updated.

If you want to know more about sending process, Please refer the datasheet here, http://www.wiznet.io/product-item/w3150a+/

Thank you


Hi, becky, hi lawrence,

thank you for your answers.

I understand now, also if i write a new value to TX_WR i can not read back this new written value, it is updated for reading with next “send” command.

This was my fault, i thougth i can read back this value always after writing.

Many thanks, Best regards, Alfred.


I made already some UDP, DHCP projekts with W3100 and W3150. But, i am not a specialist on that,. Every 5 years i have to do something.

Now i have to make migration of a produkt i did not develop ( this guy did quit years ago ) and he did not use the same drivers / software i did. He was is building up dhcp Messages in TX memory, i do not know wy.

o.k., best regards, Alfred.


hi alfred

It is great that you already made UDP, DHCP project!!

It is always hard to understand with someone’s work… haha

You will make it!!

If you have any questions, please feel free to ask !

Thank you