MAC Address

I never used this particular chip, but usually the MAC is not on chip. You have to program the chip to use the MAC you want to assign it. Methods vary from using a small serial flash to using the host processor storing it into some registers etc. The datasheet for the SMSC part you refer to surely will give you the answer.

If your question is about a ready made board you purchased somewhere, you could use a lan analyzer (

) to sniff it of the net. Provided the board uses DHCP or otherwise sends even a single frame to the net you would see it.

HTH

Markus

It has whatever MAC address you purchase and assign to it. Look at

observe that there's an EEPROM there. Your MAC lies within (or can be set from the uC's firmware).

The 91C111 does not have a MAC memory on chip.

There are two ways to load the MAC on the chip:

- SPI EEPROM connected to the chip, or - loading by software to the MAC registers directly.

You need to get a free MAC address. The addresses are administered by IEEE. Look for OUI, it's the top part of a MAC address.

For one-off projects, the simplest method by far is to hi-jack the MAC address from a throw-away NIC.

HTH

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Tauno Voipio
tauno voipio (at) iki fi

You don't even need to go that far. Just ping it from a machine and look at your ARP table. On a windoze box, use 'arp -a' after pinging it.

Regards, Mark

Or just make one up....

Youre right, but if he fidles around with network controller chips,MAC adresses and the like, chances are he will need a lan sniffer/analyzer anyways :-). Besides, etheral is free and really a plug and play experience.

Markus

It's a disaster waiting to happen. IMHO, this is not an option.

Besides, the invented address must conform to the Ethernet addressing rules, so hi-jacking is by far the easiest way, given the price of abandoned NICs.

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Tauno Voipio
tauno voipio (at) iki fi

If you don't mind using one assigned to jkmicro, send me an email and I'll give you one of mine.

Ethernet reserves the least significant bit in the first byte for multicast addresses (01-00-00-00-00-00). There are no other Ethernet addressing restrictions.

Given that MAC addresses are 48 bits long and only 1 bit is reserved for multicast addresses, there are total of 2^47-1 possible unicast addresses. Subnets normally consist of 253 or less computers, so there is an extremely good probability that a random unicast address will not conflict with already existant or future equipment. Those are good enough odds that I would bet my life on it for a one-off project.

If one really wanted to increase the odds of being unique, I'd suggest downloading the list of registered OUI's [

] and look for a company that has gone bankrupt and disappeared. A non-existant company is not likely to sue you if one of their (non-existant) users' equipment breaks because you've used their addressing space.

You might also pick up a used ISA or PCI network card from a yard sale or junk store and use that MAC.

Kelly

: >>

: >> Or just make one up.... : >

: > It's a disaster waiting to happen. IMHO, this : > is not an option. : >

: > Besides, the invented address must conform to the : > Ethernet addressing rules, so hi-jacking is by far : > the easiest way, given the price of abandoned NICs.

: Ethernet reserves the least significant bit in the first byte for multicast : addresses (01-00-00-00-00-00). There are no other Ethernet addressing : restrictions.

The second least sig bit of the first byte is also reserved for indicating administratively set MAC addresses. All allocated mac ranges have that bit set to 0. Those with long memories and networks running decnet will remember the administratively set "AA........" mac addresses decnet created.

If you invent a MAC address - set this bit.

Jim

: Given that MAC addresses are 48 bits long and only 1 bit is reserved for : multicast addresses, there are total of 2^47-1 possible unicast addresses. : Subnets normally consist of 253 or less computers, so there is an extremely : good probability that a random unicast address will not conflict with : already existant or future equipment. Those are good enough odds that I : would bet my life on it for a one-off project.

: If one really wanted to increase the odds of being unique, I'd suggest : downloading the list of registered OUI's [ :

] and look for a company that : has gone bankrupt and disappeared. A non-existant company is not likely to : sue you if one of their (non-existant) users' equipment breaks because : you've used their addressing space.

why ? Nforce2 mobos have same MACs sometimes :)

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taa

Recycling an address from an old card is fine. Problems with making one up are highly improbable these days as MAC addresses rarely have any significance outside the immediate vicinity.