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W5500 Datasheet Version1.0.9

RTR (Retry Time-value Register) [R/W] [0x0019 – 0x001A] [0x07D0]

RTR configures the retransmission timeout period. The unit of timeout period is

100us and the default of RTR is ‘0x07D0’ or ‘2000’. And so the default timeout period

is 200ms(100us X 2000).

During the time configured by RTR, W5500 waits for the peer response to the packet

that is transmitted by Sn_CR(CONNECT, DISCON, CLOSE, SEND, SEND_MAC, SEND_KEEP

command). If the peer does not respond within the RTR time, W5500 retransmits the

packet or issues timeout.

Ex) When timeout-period is set as 400ms, RTR = (400ms / 1ms) X 10 = 4000(0x0FA0)

0x0019

0x001A

0x0F

0xA0

RCR (Retry Count Register) [R/W] [0x001B] [0x08]

RCR configures the number of time of retransmission. When retransmission occurs

as many as ‘RCR+1’, Timeout interrupt is issued (Sn_IR[TIMEOUT] = ‘1’).

Ex) RCR = 0x0007

0x001B

0x07

The timeout of W5500 can be configurable with RTR and RCR. W5500 has two kind

timeout such as Address Resolution Protocol (ARP) and TCP retransmission.

At the ARP (Refer to RFC 826, http://www.ietf.org/rfc.html) retransmission timeout,

W5500 automatically sends ARP-request to the peer’s IP address in order to acquire

MAC address information (used for communication of IP, UDP, or TCP). While waiting

for ARP-response from the peer, if there is no response during the configured RTR time,

a temporary timeout is occurred and ARP-request is retransmitted. It is repeated as

many as ‘RCR + 1’ times. Even after the ARP-request retransmissions are repeated as

‘RCR+1’ and there is no response to the ARP-request, the final timeout is occurred and

Sn_IR(TIMEOUT) becomes ‘1’. The time of final timeout (ARPTO) of ARP-request is as

below.

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At the TCP packet retransmission timeout, W5500 transmits TCP packets (SYN, FIN,

RST, DATA packets) and waits for the acknowledgement (ACK) during the configured

RTR time and RCR. If there is no ACK from the peer, a temporary timeout occurs and

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