W5500 Datasheet, PDF (53/65 Pages) List of Unclassifed Manufacturers – Supports 8 independent sockets simultaneously

Sn_MSSR (Socket n Maximum Segment Size Register) [R/W] [0x0012-0x0013] [0x0000]
Sn_MSSR configures or indicates the MTU(Maximum Transfer Unit) of Socket n.
The default MTU is valid when Socket n is used in TCP / UDP mode. However, when
in PPPoE mode(MR[PPPoE] = „1‟), it is determined within PPPoE MTU.
Mode
TCP
UDP
MACRAW
Normal (MR(PPPoE)=„0‟)
PPPoE (MR(PPPoE)=„1‟)
Default MTU
Range
Default MTU
Range
1460
1 ~ 1460
1452
1 ~ 1452
1472
1 ~ 1472
1464
1 ~ 1464
1514
When Socket n is used in MACRAW mode, the default MTU is applied because the
MTU is not processed internally. Therefore, when transmitting the data bigger than
default MTU, the host should manually divide the data into the unit of default MTU.
When Socket n is used in TCP/UDP mode, and transmitting data bigger than MTU,
the data is automatically divided into the unit of MTU.
In UDP mode, because there is no such connection-process like in TCP mode, the
configured MTU is used. When transmitting data to a peer with the different MTU
size, the ICMP(Fragment MTU) packet might be received. In this case, IR(FMTU)
becomes „1‟ and the peer information such as the MTU size and IP address is
indicated from FMTUR and UIPR respectively. If IR[MTU] = „1‟, user cannot transmit
data to the peer. To resume the communication with peer, do as followed.
1. Close the Socket n by CLOSE command.
2. Set Sn_MSS to the indicated MTU from FMTUR
3. Open the Socket n by OPEN command
4. Resume the communication with the peer.
Ex) In case of Socket 0 MSS = 1460 (0x05B4), configure as below,
0x0012
0x0013
0x05
0xB4
Sn_TOS (Socket n IP Type of Service Register) [R/W] [0x0015] [0x00]
Sn_TOS configures the TOS(Type Of Service field in IP Header) of Socket n.
It is set before OPEN command.
For more the details, refer to http://www.iana.org/assignments/ip-parameters.
W5500 Datasheet Version1.0 (August 2013)
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