DM9008F datasheet(43/68 Pages) ETC

43 / 68 page

DM9008

ISA/Plug & Play Super Ethernet Contoller

Final

Version :DM9008-DS-F02

June 14, 2000

Prior to transmission, TPSR and TBCR0, TBCR1 must be

initialized. To initiate transmission of the packet, the TXP bit in

the Command Register is set. The Transmit Status Register

(TSR) is cleared and DM9008 begins to transmit data from

memory (unless the ENC is currently receiving). If the

interframe gap has timed out, ENC will begin transmission.

Collision Recovery

During transmission, Buffer Management logic monitors the

transmit circuitry to determine whether a collision has

occurred. If a collision is detected, the Buffer Management

logic will reset the FIFO and restore the Transmit DMA pointers

for retransmission of the packet. The COL bit will be set in TSR

and NCR (Number of Collisions Register) will be incremented.

If 15 successive retransmissions each result in a collision, the

transmission will be aborted and the ABT bit in TSR will be set.

Note: NCR reads as all zeroes if excessive collisions are

encountered.

Transmit Packet Assembly Format

The following diagrams describe the format for assembling

packets prior to transmission for different byte ordering

schemes. The various formats are selected in the DCR.

D15

DA1

DA0

DA3

DA2

DA5

DA4

SA1

SA0

SA3

SA2

SA5

SA4

T/L1

T/L0

DATA1

DATA0

BOS=0, WTS=1 in DCR

This format is used with Series 32000 808X-type processors.

D15

DA0

DA1

DA2

DA3

DA4

DA5

SA0

SA1

SA2

SA3

SA4

SA5

T/L0

T/L1

DATA0

DATA1

BOS =1, WTS = 1 in DCR

This format is used with 68000-type processors.

DA0

DA1

DA2

DA3

DA4

DA5

SA0

SA1

BOS = 0, WTS = 0 in DCR

This format is used with general 8-bit CPUs.

Loopback Diagnostics

Three forms of local loopback are provided on the DM9008.

The user has the ability to loop back through the deserializer

on the ENC, through the ENA, and to the co-ax to check the

link via the transceiver circuitry. Because of the half duplex

architecture of DM9008, loopback testing is a special mode of

operation.

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