Acromag 900EN-S005, User Manual

Page: 26 / 64

BusWorks
®
900EN-S005 Ethernet Switch User’s Manual Ethernet I/O
__________________________________________________________________
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Acromag, Inc. Tel:248-624-1541 Fax:248-624-9234 Email:
sales@acromag.com http://www.acromag.com
26
REG DESCRIPTION DEF
3 03H Global Control 1…continued 04H
Bit Function
3 Frame Length Field Check:
1=Check the frame length field in the IEEE packets,
and if the actual length does not match, the
packet will be dropped (for L < 1500).
0=Do not check frame length.
0
2 Aging Enable:
1=Enable aging (default aging period is 300±75s).
0=Disable aging.
This function may optionally be controlled via
DIP switch 1.
1/0
1 Fast Aging Enable: 1=Turn on fast aging (~800us);
0=Standard aging (300±75s). See Note at left. 0
0 Aggressive Back-Off Enable (Half-Duplex):
1=Enable the more aggressive back-off algorithm in
half-duplex mode to enhance performance (this is
not an IEEE standard). Default is ON in
EEPROM mode and OFF in DIP Switch Mode.
0=Disable aggressive back-off.
This function may optionally be controlled via
DIP switch S1-5 which is OFF by default.
0/1
4 04H Global Control 2 F0H
Bit Function
7 Unicast Port-VLAN Mismatch Discard. This feature
is used for port-VLAN’s (see registers 17 and 33).
1=All packets cannot cross VLAN boundary.
0=Unicast packets (excluding unknown/multicast/
broadcast) can cross VLAN boundary.
1
6 Multicast Storm Protection Disable:
1=Broadcast Storm Protection does not include
multicast packets. Only DA=FFFFFFFFFFFF
packets will be regulated.
0=Broadcast Storm Protection includes
DA=FFFFFFFFFFFF and DA[40]=1 packets.
1
5 Back Pressure Mode:
1=Carrier sense back-pressure is selected.
0=Collision based back-pressure is selected. 1
4 Flow Control & Back Pressure Fair Mode:
1=Fair Mode is selected. In this mode, if a flow
control port and a non-flow control port talk to the
same destination port, packets from the non-flow
control port may be dropped. This is to prevent
the flow control port from being flow controlled for
an extended period of time.
0=In non-fair mode, if a flow control port and a non-
flow control port talk to the same destination port,
the flow control port will be flow controlled. This
may not be “fair” to the flow control port.
1
Register Map
Note: Excessive use of fast
aging can make your switch
act more like a hub. Recall
that a switch will send a
message to all switch ports
(like a hub does), until it
actually learns an address
(usually after the first
communication). If fast aging
is enabled and messages
happen to be infrequent
(reoccurring after 800us), then
the switch will age out a
learned address, and revert to
sending a subsequent
message to all ports, rather
than the target port. This
makes data transfer less
efficient and needlessly
increases network traffic.