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W5500 Datasheet Version1.0.9

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

Description

0x01

OPEN

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 (0x42)

0x02

LISTEN

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.

0x04

CONNECT

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 ARPTO 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 TCPTO (Sn_IR(3) =

‘1 )

3. When a RST packet is received instead of a SYN/ACK packet.

W5500 Datasheet(PDF) 46 Page - WIZnet Co., Ltd

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