W5200 datasheet(62/88 Pages) WIZNET

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5.2.2.2

Multicast

The broadcast communication communicates with many and unspecified others. But the

multicast communication communicates with many specified others who registered at a

multicast-group. Suppose that A, B, and C are registered at a specified multicast-group.

If user transmits data to multicast-group (contains A), B and C also receive the DATA for

A. To use multicast communication, the destination list registers to multicast-group by

using IGMP protocol. The multicast-group consists of ‘Group hardware address,’ ‘Group

IP address,’ and ‘Group port number.’ User cannot change the ‘Group hardware address’

and ‘Group IP address.’ But the ‘Group port number’ can be changed.

The ‘Group hardware address’ is selected at the assigned range (From

“01:00:5e:00:00:00”to “01:00:5e:7f:ff:ff”) and the ‘Group IP address’ is selected in D-

class IP address (From “224.0.0.0” to “239.255.255.255”, please refer to the website;

http://www.iana.org/assignments/multicast-addresses

When selecting, the upper 23bit of 6bytes ‘Group hardware address’ and the 4bytes

‘Group IP address’ must be the same. For example, if the user selects the ‘Group IP

address’ to

“244.1.1.11,”

the

‘Group

hardware

address’ is

selected

“01:00:5e:01:01:0b.” Please refer to the “RFC1112” (

http://www.ietf.org/rfc.html

In the W5200, IGMP processing to register the multicast-group is internally

(automatically) processed. When the user opens the Socket n with multicast mode,

the “Join” message is internally transmitted. If the user closes it, the “Leave” message

is internally transmitted. After the SOCKET opens, the “Report” message is periodically

and internally transmitted when the user communicates.

The W5200 support IGMP version 1 and version 2 only. If user wants use an updated

version, the host processes IGMP directly by using the IPRAW mode SOCKET.

SOCKET Initialization

Choose one SOCKET for multicast communication among 8 SOCKETS of W5200. Set the

Sn_DHAR0 to ‘Multicast-group hardware address’ and set the Sn_DIPR0 to ‘Multicast-

group IP address.’ Then set the Sn_PORT0 and Sn_DPORT0 to ‘Multicast-group port

number.’ Set the Sn_MR(P3:P0) to UDP and set the Sn_MR(MULTI) to ‘1.’ Finally, execute

OPEN command. If the state of Sn_SR is changed to SOCK_UDP after the OPEN command,

the SOCKET initialization is completed.

{

START:

/* set Multicast-Group information */

Sn_DHAR0 = 0x01;

/* set Multicast-Group H/W address(01:00:5e:01:01:0b) */

Sn_DHAR1 = 0x00;

Sn_DHAR2 = 0x5E;

Sn_DHAR3 = 0x01;

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