TNETX3150 Datasheet, PDF (35/113 Pages) Texas Instruments – ThunderSWITCHE 15-PORT 10-/100-MBIT/S ETHERNETE SWITCH

TNETX3150/TNETX3150A
ThunderSWITCH^™ 15-PORT 10-/100-MBIT/S ETHERNET^™ SWITCH
SPWS027F – FEBRUARY 1997 – REVISED SEPTEMBER 1997
DRAM and EAM interfaces (continued)
The TNETX3150/TNETX3150A uses the external channel address, in priority over the internal channel address
match information, to route the frame to the appropriate channel. To disable the EAM interface, the no-operation
code should be used. If there is no EAM hardware present, the no-operation code should be hardwired onto
the interface. The no-operation code causes the internal destination selection to be used. See Figure 14.
EAM
Hardware
(External Address
Lookup Device)
EAM15 (mode select)
EAM14
EAM00
TNETX3150/TNETX3150A
EDO
DRAM
DD35–DD00
DA7–DA0
DX2–DX0
DRAS
DCAS
DWE
DOE
Figure 14. EAM Interface
Table 6 provides the 4-bit code needed to identify the destination port when using the EAM interface with EAM15
(mode select) bit set.
D With the EAM04 bit and EAM15 bit (mode select) both set, all other EAM bits are ignored (this is a
no-operation code) and the frame uses the internal address match information (if enabled). With this code,
any external device is signaling that it does not participate in address matching (at least during this cycle).
These two bits need to be hardwired to 1 if no external device is present to disable this interface.
D With the EAM04 bit reset and EAM15 bit (mode select) set, EAM03–EAM00 code is used to identify a single
destination port.
When the EAM15 bit (mode select) is reset:
D The other bits EAM14–EAM00 represent a mask of the ports to which the frame is forwarded. For example,
if the frame is copied to ports 00, 07, and 14, the value signaled is 0x4081 or 0b0100000010000001.
D To discard a frame, the external interface provides an all-zero code (0x0000 or 0b0000000000000000),
which indicates that the external device is going to specify all the ports to forward the frame to, and there
are no valid 1s for this frame.
All internal address registers should be disabled with the address-disable bit (port-control register bit 3), if the
external device is used.
An external device has the choice of two codes to forward a frame to a single port. To forward to port 3, one can
enter 0x0004 (multiport capable with only one port specified), or 0x8003 (single-port capable only). While using
the first method can make specifying unicast and multicast forwarding more unified, it forces the
TNETX3150/TNETX3150A to use internal cycles to build an IOB table with only one entry, and thereby unicast
traffic takes a large drop in performance. Unicast forwarding is done with the EAM15 set, and the port specified
in the lower four bits.
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