1000Base-T MagJacks, no. of cores, LED colours - Page 1
Forum section: electronics / projects

author: Northy
author_rank: Regular Contributor
timestamp: October 19, 2020, 01:44:33 pm
content: I seem to have spent all morning looking at Magjacks!Who knew there was so much to them?Can someone please explain the difference between the number of cores? The two popular ones seem to be 8 or 12 cores per port.Is there a standard conversion for LED colours at all? I need to signify 10/100 or 100Base-T link/activity.Thanks,G

author: Miyuki
author_rank: Frequent Contributor
timestamp: October 19, 2020, 01:52:36 pm
content: There is no real conventionSame with activity signalisationEvery big company have its own way

author: phil from seattle
author_rank: Super Contributor
timestamp: October 19, 2020, 03:37:34 pm
content: Funny, I've spent the last couple of days doing the same though my goal is to figure out the best magjack for manufacturing a board in china. I was really hoping to find several that have the same pinout (for manufacturing flexibility) but even within a single manufacturer, the pinouts seem to all be different. I was also hoping to find horizonal entry and vertical entry jacks with the same pinout as I have some customers asking for each but no love there. Hate to have two different PCBs but it looks like that's going to be the case. sigh.

author: niconiconi
author_rank: Frequent Contributor
timestamp: October 19, 2020, 03:52:53 pm
content: Quote from: Northy on October 19, 2020, 01:44:33 pmThere isn't much of a difference, the only difference is that the 8-core magnetics only have a group of common-mode chokes for EMI suppression, but the 12-core magnetics have both a group of common-mode choke and a group of center-tapped autotransformers to suppress EMI better (both are common-mode noise suppressors). A 12-core Magjack is usually recommended due to its better EMC performance. But if you must use a 8-core version, it should work too.The 8-core magnetics basically has:CM Choke (x4) - 1:1 Transformer (x4) - ConnectorAnd the 12-core magnetics:CM Choke (x4) - 1:1 Transformer (x4) - Autotransformer (x4) - ConnectorCheck this Application Note fromMicrosemiMicrochip:https://www.infinite-electronic.my/datasheet/29-VSC8540XMV-03.pdf

author: Northy
author_rank: Regular Contributor
timestamp: October 19, 2020, 09:14:52 pm
content: Thanks for all the replies so farLooks like I want to find a 12 core part then.I feel a bit like I've gone round in circles today.What colour LEDs do people think are sensible?The switch IC I'm using is designed to drive a bi-colour LED to show 10/100/1000 connection and activity all on the one (bi-colour) LED!G

author: Northy
author_rank: Regular Contributor
timestamp: October 20, 2020, 08:14:21 am
content: I got a reply back from a connector manufacturer:Currently. we will not promote 12 cores / 1000 base-T part to customer side. Since 8 cores’ design performance can have the same performance and have price competitive.So, what are peoples feelings on 12 cores? Does no-one actually use them in reality?With good layout etc is 8 core generally ok?G

author: tszaboo
author_rank: Super Contributor
timestamp: October 20, 2020, 08:31:28 am
content: Quote from: Northy on October 20, 2020, 08:14:21 amhttps://www.we-online.com/catalog/media/o119947v446%20Tutorials_High%20Performance%20Low%20EMI%20Series_EN%20(rev1).pdfIf you check the CMR and other graphs, you will see that the 12 core versions have higher attenuation in the 100MHz-500MHz range. 8 core might fail the EMC susceptibility tests, the 12 core might pass.

author: Northy
author_rank: Regular Contributor
timestamp: October 21, 2020, 08:25:28 am
content: Does anyone here use magjacks in products?Do you se 8 core or 12 core?Thanks,G

author: Ranayna
author_rank: Super Contributor
timestamp: October 21, 2020, 10:16:56 am
content: Regarding LED colors:In networking gear i almost always see orange for 10/100 and green for 1000 as link speed indicator. In clients it is generally green for 1000 as well, but i don't recall when i saw a gigabit capable client only using 10/100.For activity it is green as well, most of the time.Offhand, i can't name a specific device that uses different colors.

author: Scrts
author_rank: Frequent Contributor
timestamp: October 21, 2020, 02:53:59 pm
content: Please be aware that some MagJacks are for PHY voltage outputs and some are for current outputs. I've made that mistake once... I highly recommend checking with the PHY supplier what are the recommended MagJacks or look into reference designs.As for the colors, I usually like 1 or 2 Dual LEDs, so you can change color depending on link and/or activity.

author: Northy
author_rank: Regular Contributor
timestamp: October 21, 2020, 06:53:18 pm
content: Thank you both for the replies.Have you had success passing EMC testing with 8 core parts?G

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 23, 2020, 08:35:03 pm
content: Quote from: Northy on October 21, 2020, 06:53:18 pmPersonally I like: led1 green-link (regardless of speed), led2 yellow-flashing activity.