Datasheet
Table Of Contents
38 / 66 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 (ARP
TO
) of ARP-request is as
below.
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