DP83901AV datasheet(26/62 Pages) NSC

26 / 62 page

100 Internal Registers (Continued)

103 REGISTER DESCRIPTIONS

(Continued)

TRANSMIT CONFIGURATION REGISTER (TCR)

0DH (WRITE)

The transmit configuration establishes the actions of the transmitter section of the SNIC during transmission of a packet on the

network LB1 and LB0 which select loopback mode power up as 0

76543210

OFST

ATD

LB1

LB0

CRC

Bit

Symbol

Description

CRC

Inhibit CRC

0 CRC appended by transmitter

1 CRC inhibited by transmitter

In loopback mode CRC can be enabled or disabled to test the CRC logic

LB0

Encoded Loopback Control

These encoded configuration bits set the type of loopback that is to be

performed Note that loopback in mode 2 places the ENDEC Module in loopback mode and that D3 of the

and

DCR must be set to zero for loopback operation

LB1

LB0

Mode 0

Normal Operation (LPBK e 0)

Mode 1

Internal NIC Module Loopback (LPBK e 0)

Mode 2

Internal ENDEC Module Loopback (LPBK e 1)

Mode 3

External Loopback (LPBK e 0)

ATD

Auto Transmit Disable

This bit allows another station to disable the SNIC’s transmitter by transmission of a

particular multicast packet The transmitter can be re-enabled by resetting this bit or by reception of a

second particular multicast packet

1 Reception of multicast address hashing to bit 62 disables transmitter reception of multicast address

hashing to bit 63 enables transmitter

OFST

Collision Offset Enable

This bit modifies the backoff algorithm to allow prioritization of nodes

0 Backoff Logic implements normal algorithm

1 Forces Backoff algorithm modification to 0 to 2min(3an 10) slot times for first three collisions then follows

standard backoff (For the first three collisions the station has higher average backoff delay making a low

priority mode)

Reserved

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