W5500 Datasheet, PDF (55/65 Pages) List of Unclassifed Manufacturers – Supports 8 independent sockets simultaneously

Socket n TX Buffer Block can be accessible with 16bits Offset Address ranged
from 0x0000 to 0xFFFF regardless of the configured size. (Refer to Sn_TX_WR &
Sn_TX_RD).
Value (dec)
0
1
2
4
8
16
Buffer size
0KB
1KB
2KB
4KB
8KB
16KB
Ex) Socket 0 TX Buffer Size = 4KB
0x001F
0x04
Sn_TX_FSR (Socket n TX Free Size Register) [R] [0x0020-0x0021] [0x0800]
Sn_TX_FSR indicates the free size of Socket n TX Buffer Block. It is initialized to
the configured size by Sn_TXBUF_SIZE. Data bigger than Sn_TX_FSR should not be
saved in the Socket n TX Buffer because the bigger data overwrites the previous
saved data not yet sent. Therefore, check before saving the data to the Socket n TX
Buffer, and if data is equal or smaller than its checked size, transmit the data with
SEND/SEND_MAC command after saving the data in Socket n TX buffer. But, if data is
bigger than its checked size, transmit the data after dividing into the checked size
and saving in the Socket n TX buffer.
If Sn_MR(P[3:0]) is not TCP mode(„0001‟), it is automatically calculated as the
difference between „Socket n TX Write Pointer (Sn_TX_WR)‟ and „Socket n TX Read
Pointer (Sn_TX_RD)‟.
If Sn_MR(P[3:0]) is TCP mode(„0001‟), it is automatically calculated as the
difference between Sn_TX_WR and the internal ACK pointer which indicates the
point of data is received already by the connected peer.
Ex) In case of 2048(0x0800) in S0_TX_FSR,
0x0020
0x0021
0x08
0x00
Sn_TX_RD (Socket n TX Read Pointer Register) [R] [0x0022-0x0023] [0x0000]
Sn_TX_RD is initialized by OPEN command. However, if Sn_MR(P[3:0]) is TCP
mode(„0001‟), it is re-initialized while connecting with TCP.
After its initialization, it is auto-increased by SEND command. SEND command
transmits the saved data from the current Sn_TX_RD to the Sn_TX_WR in the Socket
n TX Buffer. After transmitting the saved data, the SEND command increases the
Sn_TX_RD as same as the Sn_TX_WR. If its increment value exceeds the maximum
W5500 Datasheet Version1.0 (August 2013)
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