W5100 datasheet(35/72 Pages) WIZNET

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Sn_TX_RR (Socket n TX Read Pointer Register) [R] [0x0422-0x0423, 0x0522-0x0523,

0x0622-0x0623, 0x0722-0x0723] [0x0000]

This register shows the address that transmission is finished at the TX Memory. With the SEND

command of Socket n Command Register, it transmits data from current Sn_TX_RR to

Sn_TX_WR and automatically changes after transmission is finished. Therefore, after

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

(0x0423, 0x0523, 0x0623, 0x0723) later to get the correct value.

Sn_TX_WR (Socket n TX Write Pointer Register) [R/W] [0x0424-0x0425, 0x0524-0x0525,

0x0624-0x0625, 0x0724-0x0725] [0x0000]

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

(0x0425, 0x0525, 0x0625, 0x0725) later to get the correct value.

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

Sn_CR.

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

0x0424

0x0425

0x08

0x00

But this value itself is not the physical address to write. So, the physical address should be

calculated as follow.

1. Socket n TX Base Address (hereafter we'll call gSn_TX_BASE) and Socket n TX Mask

Address (hereafter we'll call gSn_TX_MASK) are calculated on TMSR value. Refer to

the psedo code of the Initialization if the detail is needed.

2. The bitwise-AND operation of two values, Sn_TX_WR and gSn_TX_MASK give result

the offset address(hereafter we'll call get_offset) in TX memory range of the socket.

3. Two values get_offset and gSn_TX_BASE are added together to give result the

physical address(hereafter, we'll call get_start_address).

Now, write the transmission data to get_start_address as large as you want. (* There's a case

that it exceeds the TX memory upper-bound of the socket while writing. In this case, write

the transmission data to the upper-bound, and change the physical address to the

gSn_TX_BASE. Next, write the rest of the transmission data.)

After that, be sure to increase the Sn_TX_WR value as much as the data size that indicates

the size of writing data. Finally, give SEND command to Sn_CR(Socket n Command Register).

Refer to the psedo code of the transmission part on TCP Server mode if the detail is needed.

W5100 Datasheet(PDF) 35 Page - WIZnet Co., Ltd