---
title: "Mismatch between TCPTO formula and example in datasheet?"
url: "https://maker.wiznet.io/forum/14473"
markdown_url: "https://maker.wiznet.io/forum/14473/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "JOB"
created: "2022-02-10T15:15:43+09:00"
last_activity: "2022-02-10T15:15:43+09:00"
language: "en"
views: 317
replies: 0
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Mismatch between TCPTO formula and example in datasheet?

## Question

Asked by JOB on 2022-02-10 in Ethernet Chips.

When I try to calculate the TCPTO for W5500 from formula on page 39 of datasheet version 1.0.9, using the values given in the example (RTR = 2000 and RCR = 8), I get for the second term: (𝑅𝐶𝑅 − 𝑀) × 𝑅𝑇𝑅𝑀𝐴𝑋 = (𝑅𝐶𝑅 − 𝑀) × 𝑅𝑇𝑅 × 2^𝑀 = (8 - 4) x 2000 x 2^4 = (8 - 4) x **32000**. However, the datasheet gives for this second term: (8 - 4) x **64000**.
Am I wrong or should 𝑅𝑇𝑅𝑀𝐴𝑋 be: 𝑅𝑇𝑅𝑀𝐴𝑋 = 𝑅𝑇𝑅 × 2^(**𝑀+1**)?

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Source: https://maker.wiznet.io/forum/14473