TNETX3100 datasheet(21/80 Pages) TI1

21 / 80 page

TNETX3100

ThunderSWITCH™ 10-PORT 10-/100-MBIT/S ETHERNET™ SWITCH

SPWS031D – JUNE 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

DRAM and EAM interfaces (continued)

The TNETX3100 gives priority to the external channel address, over the internal-channel address-match in-

formation, to route the frame to the appropriate channel. To enable the EAM interface, the EAMON bit in the

FEAGFG register must be set to a 1 (see Figure 8).

EAM

Hardware

EAM15 (mode select)

EAM09

EAM00

DD(35–00)

DA(7–0)

DX(2–0)

DRAS

DCAS

DWE

DOE

TNETX3100

EDO

DRAM

Figure 8. EAM Interface

Table 2 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 high, 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 are hardwired to 1 if no external device is present to disable this interface.

D With the EAM04 bit low and EAM15 bit (mode select) high, EAM03–EAM00 code is used to identify a single

destination port.

D When the EAM15 bit (mode select) is low:

–

The other bits EAM09–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 09, the signal value is 0b1010000001.

–

To discard a frame, the external interface provides an all-zero code 0b0000000000).

All internal-address registers are disabled with the not-learn (NLEARN) bit (port-control register, bit 3), if the

external device is used.

An external device has two choices of codes with which to forward a frame to a single port. For example, to

forward a frame to port 3, one can enter 0x004 (multiport capable with only one port specified), or 0x403

(single-port capable only). While using the first method can make specifying unicast and multicast forwarding

more unified, it forces the TNETX3100 to use internal cycles to build a broadcast table with only one entry, and

thereby unicast traffic performance is reduced. Unicast forwarding is done with the EAM15 high, and the port

specified in the lower four bits.

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