How to make a fast ethernet loopback cable

#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SERIAL#
#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SOFTWARE#
#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE CODE#
#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SERIES#

The challenges would lie in creating a reliable, interference free design that could cope with the high-frequency ethernet signals.

#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SOFTWARE#

Well, we have a micrcontroller and rather a good one at that, so weвЂ™ll be configuring the registers to known values through software after a hard reset.ДЄfter reading the datasheet, and the application notes on MicrelвЂ™s website, I decided that a development board should not be too hard to design.

#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE CODE#

Code not written is flash memory not used is money saved. That means that a low-cost board could configure the PHY by setting appropriate pull-ups and pull-downs on the pins and thereby not have to write microcontroller code to configure the device through software. Rather than hardcode some defaults, the device uses the rather ingenious method of momentarily sampling the levels (high or low) of a selection of its pins and using those levels to configure the registers. Upon power-up or hard reset the PHY has to configure its internal registers with some default values.

On-chip termination resistors for the differential pairs.

Single 3.3V (or 2.5V or 1.8V) power input вЂ“ the 1.2V regulator is built in.

Diagnostics for detecting where a cable fault lies, and diagnostics for detecting pin-to-board faults.

Power saving modes вЂ“ ethernet is quite power-hungry when itвЂ™s active.

Auto detection of straight-through and crossover cables so you can use either type.

LED outputs for link, speed and activity status.

Interrupt support so we donвЂ™t have to continually poll the device to find out when something has happened.

HereвЂ™s a functional diagram of the KSZ8051MLL taken from the datasheet that shows how it fits into the ethernet physical layer.ДЄs well as providing the core PHY support the KSZ8051MLL has some useful extra features: The KSZ8051MLL in LQFP48 7x7mm package, 0.5mm pitch. Yes, 86 pence is all you need to fork out for the core IC in a PHY. The one I selected is the Micrel KSZ8051MLL, available at the time of writing from Farnell in single units for 86p. They all implement the basic protocol and then add various extras such as indicator LEDs, error detection and various types of auto-detection of your configuration. ThereвЂ™s a few of them to choose from, and theyвЂ™re all much of a muchness, I mean how exciting can you make an ethernet 10/100 transceiver? вЂNot veryвЂ™ is the answer to that question. This article will focus on building a PHY targeted at the STM32F107 but compatible with any MCU that can talk the MII protocol.

#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SERIAL#

If you donвЂ™t have ethernet support on your MCU then this is what you could use, but it will cost a little more due to the increased feature set and the interface is likely to be serial which may limit performance.ДЄnother option is to buy the ST official PHY add-on board for their F107 development board but itвЂ™s pricey, and itвЂ™s much more fun to build your own.

Companies such as Wiznet with their W5100 device have taken the logical step of integrating the MAC, PHY and the entire TCP stack into one IC. If you donвЂ™t happen to have one of those then all is not lost. ThereвЂ™s an STM32F107 modestly hiding behind the faded print

#HOW TO MAKE A FAST ETHERNET LOOPBACK CABLE SERIES#

Ethernet tends to feature in special series MCUs or newer and more expensive devices. The STM32F107 is one, the STM32F2 and STM32F4 series are others. Only a minority of MCUs have ethernet support. This separation of concerns reduces overall cost by limiting the complexity of the components outside the MCU. It also does the reverse, decoding incoming signals from the RJ45 connector and talking MII back to the MCU. The PHY receives the 4-bit wide MII protocol and synthesises the differential signals necessary to drive the ethernet RJ45 socket.

The MCU provides a 10/100Mbs MAC and can talk the standard Media Independent Interface (MII) protocol to the outside world. MCUs such as the STM32F107 come with a degree of ethernet support built-in.

Well, itвЂ™s the physical transceiver that converts a well-known data-bus protocol implemented by your MCU into the physical signals that go down the wire. A what? If youвЂ™ve never crossed paths with ethernet technologies before then you may not know what an ethernet PHY is.

How to make a fast ethernet loopback cable