W5500 Datasheet, PDF (46/65 Pages) List of Unclassifed Manufacturers – Supports 8 independent sockets simultaneously

Sn_CR (Socket n Command Register) [R/W] [0x0001] [0x00]
This is used to set the command for Socket n such as OPEN, CLOSE, CONNECT,
LISTEN, SEND, and RECEIVE. After W5500 accepts the command, the Sn_CR register is
automatically cleared to 0x00. Even though Sn_CR is cleared to 0x00, the command
is still being processed. To check whether the command is completed or not, please
check the Sn_IR or Sn_SR.
Value
Symbol
0x01
OPEN
0x02
LISTEN
0x04
CONNECT
Description
Socket n is initialized and opened according to the protocol
selected in Sn_MR (P3:P0). The table below shows the value of
Sn_SR corresponding to Sn_MR.
Sn_MR (P[3:0])
Sn_SR
Sn_MR_CLOSE („0000‟)
-
Sn_MR_TCP („0001‟)
SOCK_INIT (0x13)
Sn_MR_UDP („0010‟)
SOCK_UDP (0x22)
S0_MR_MACRAW („0100‟)
SOCK_MACRAW (0x02)
.
This is valid only in TCP mode (Sn_MR(P3:P0) = Sn_MR_TCP). In this
mode, Socket n operates as a „TCP server‟ and waits for
connection-request (SYN packet) from any „TCP client‟.
The Sn_SR changes the state from SOCK_INIT to SOCKET_LISTEN.
When a „TCP client‟ connection request is successfully established,
the Sn_SR changes from SOCK_LISTEN to SOCK_ESTABLISHED and the
Sn_IR(0) becomes „1‟. But when a „TCP client‟ connection request is
failed, Sn_IR(3) becomes „1‟ and the status of Sn_SR changes to
SOCK_CLOSED.
This is valid only in TCP mode and operates when Socket n acts as
„TCP client‟. To connect, a connect-request (SYN packet) is sent to
„TCP server‟ configured by Sn_DIPR & Sn_DPORT(destination address
& port). If the connect-request is successful, the Sn_SR is changed
to SOCK_ESTABLISHED and the Sn_IR(0) becomes „1‟.
The connect-request fails in the following three cases.
1. When a ARP_TO occurs (Sn_IR(3)=„1‟) because the destination
hardware address is not acquired through the ARP-process.
2. When a SYN/ACK packet is not received and TCP_TO (Sn_IR(3) =
„1 )
3. When a RST packet is received instead of a SYN/ACK packet.
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W5500 Datasheet Version1.0 (August 2013)