---
title: "Unable to read the TX Buffer of w5500"
url: "https://maker.wiznet.io/forum/12356"
markdown_url: "https://maker.wiznet.io/forum/12356/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "dhanunjay"
created: "2017-07-06T05:05:16+09:00"
last_activity: "2017-07-07T04:31:03+09:00"
language: "en"
views: 1444
replies: 2
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Unable to read the TX Buffer of w5500

## Question

Asked by dhanunjay on 2017-07-06 in Ethernet Chips.

Hi,

I wanted to read the data i have written o the buffer, but when ever i read the pointers RD and WR both are same at every point and i am using wiz_send_data() for writing and wiz_read_buffer() for reading it back.
But when the change the command register value to the send_command i am observing the packet on the wireshark with the data i am writing over the buffer.

## Replies

### Reply 1 by jim, 2017-07-06

Dear dhanunjay

What kind of type is your MCU?
First of all, please check SPI operation between MCU and W5500. Is it work?
And then refer to loopback_tcps() function in loopback.c file. ([GitHub - Wiznet/ioLibrary_Driver: ioLibrary_Driver can be used for the application design of WIZnet TCP/IP chips as W5500, W5300, W5200, W5100 W5100S.](https://github.com/Wiznet/ioLibrary_Driver) )

The following all cases were released products.
NXP case:
Please refer to SPI Interface in [GitHub - Wiznet/WIZ550S2E: Serial to Ethernet Module based on W5500 & Cortex-M0](https://github.com/Wiznet/WIZ550S2E) or [GitHub - Wiznet/W5500_EVB: W5500-EVB Library and Examples](https://github.com/Wiznet/W5500_EVB)

ST case:
Refer to SPI Interface in [GitHub - Wiznet/WIZ550SR: Serial to Ethernet Module based on W5500 & Cortex-M3](https://github.com/Wiznet/WIZ550SR) or [GitHub - Wiznet/WIZ550web: Webserver application with W5500 for things (Non-OS)](https://github.com/Wiznet/WIZ550web)

And last, please confirm schematic files by WIZnet. (support@wiznet.io)

Thanks.

### Reply 2 by dhanunjay, 2017-07-07 (in reply to reply 1)

Hi jim,

I am using pic18f45k22 micro controllers. SPI between pic and w5500 is working, i have tested the loopback tcp.
Problem is i am unable to send the a TCP Packet with size of 1514 bytes. I am trying to fill the TX buffer with 1460 and then change the command register to the send command. but when i did that i am only seeing the last set i am writing to the TX buffer.

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Source: https://maker.wiznet.io/forum/12356