DFRobot Ethernet W5200 Shield for Arduino : Data Sheet : Page 38

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Sn_TX_FSR (Socket n TX Free Size Register) [R] [0x4020+0x0n00-0x4021+0x0n00]

[0x0800]

It notifies the available size of the internal TX memory (the byte size of transmittable data)

of Socket n . The host can’t write data as a size bigger than Sn_TX_FSR. Therefore, be sure to

check Sn_TX_FSR before transmitting data, and if your data size is smaller than or the same

as Sn_TX_FSR, transmit the data with SEND or SEND_MAC command after copying the data.

At the TCP mode, if the peer checks the transmitted DATA packet (if DATA/ACK packet is

received from the peer), Sn_TX_FSR is automatically increased by the size of that transmitted

DATA packet. At the other modes, when Sn_IR(SENDOK) is ‘1’, Sn_TX_FSR is automatically

increased by the size of the transmitted data.When checking this register, user should read

upper byte(0x4020, 0x4120, 0x4220, 0x4320, 0x4420, 0x4520, 0x4620, 0x4720) first and lower

byte(0x4021, 0x4121, 0x4221, 0x4321, 0x4421, 0x4521, 0x4621, 0x4721) later to get the

correct value.

Ex) In case of 2048(0x0800) in S0_TX_FSR,

0x4020 0x4021

0x08 0x00

Sn_TX_RD (Socket n TX Read Pointer Register) [R] [0x4022+0x0n00-0x4023+0x0n00]

[0x0000]

This register shows the address of the last transmission finishing in the TX memory. With the

SEND command of Socket n Command Register, it transmits data from the current Sn_TX_RD

to the Sn_TX_WR and automatically updates after transmission is finished. Therefore, after

transmission is finished, Sn_TX_RD and Sn_TX_WR will have the same value. When reading this

register, user should read upper byte (0x4022, 0x4122, 0x4222, 0x4322, 0x4422, 0x4522,

0x4622, 0x4722) first, and lower byte (0x4023, 0x4123, 0x4223, 0x4323, 0x4423, 0x4523,

0x4623, 0x4723) later to get the correct value.

Sn_TX_WR (Socket n TX Write Pointer Register) [R/W] [0x4024+0x0n00-0x4025+0x0n00]

[0x0000]

This register offers the location information to write the transmission data. When reading this

register, user should read upper byte (0x4024, 0x4124, 0x4224, 0x4324, 0x4424, 0x4524,

0x4624, 0x4724) first, and lower byte (0x4025, 0x4125, 0x4225, 0x4325, 0x4425, 0x4525,

0x4625, 0x4725) later to get the correct value.

Caution: This register value is changed after the send command is successfully executed to

Sn_CR.

Ex) In case of 2048(0x0800) in S0_TX_WR,

0x4024 0x4025

0x08 0x00