GE GFK-1541B manual MAC Addresses

6

MAC Addresses

Note

It is highly recommended that you use the unique default MAC supplied within the Ethernet Interface. However, you may override that default with a MAC address of your own choosing with the Station Manager CHPARM MACADDR command (See GFK-1186, TCP/IP Ethernet Communications for the Series 90 PLC Station Manager Manual.)

The MAC address is a 48-bit binary number that identifies the station on the physical network. The MAC address is typically expressed as a 12-digit hexadecimal number. A typical MAC address is represented as follows:

Byte		1		2		3		4		5		6
	________ _________ _________ _________ _________ _________
Hex	0	8	0	0	1	9	0	1	5	3	1	2
Binary	0000	1000	0000	0000	0001	1001	0000	0001	0101	0011	0001	0010

Another characteristic that is important, especially for multi-vendor networks, is the order of address-bit transmission on the physical medium. MAC addresses are transmitted in ascending byte order, with the least significant bit of each byte transmitted first.

The example above is shown including bit transmission order as follows:

Byte		1		2		3		4		5		6
	________		_________		_________		_________ _________				_________
Hex	0	8	0	0	1	9	0	1	5	3	1	2
Binary	0000	1000	0000	0000	0001	1001	0000	0001 0101		0011	0001	0010
Bit Order 8765		4321		...9
									MSB of the MAC
LSB of the MAC address-first bit transmitted									address-last bit
									transmitted

If you assign your own MAC addresses, there are 2 bits of the 48-bit address that you must set according to the instructions that follow:

ƒBit 1 in Byte 1 must always be a 0 to indicate an individual station rather than a Group address.

ƒBit 2 in Byte 1 must be a 1 to indicate that the address is locally administered. (In the typical default MAC address shown above, bit 2 in Byte 1 is a 0 indicating that it is a globally administered address).

ƒAll other bits can be set as desired as long as all stations on the network have unique addresses.

An example of a locally administered MAC address is shown below.

Byte		1		2		3		4		5		6
	________ _________				_________		_________ _________				_________
Hex	0	2	0	0	0	0	0	0	0	1	0	0
Binary	0000	0010	0000	0000	0000	0000	0000	0000	0000	0001	0000	0000
Bit Order 8765		4321		...9
											MSB of the
LSB of the MAC address-first bit transmitted											MAC address-last
											bit transmitted

If you must change the Station MAC address, check with the person administering your network to make sure that you select an address that fits into your local administration scheme.

6-12 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual– May 2002 GFK-1541B