Datasheet

78Q2120C

10/100BASE-TX

Transceiver

MR0: Control Register (continued)

BIT SYMBOL TYPE DEFAULT DESCRIPTION

0.8 DUPLEX R/W (1)

Duplex Mode: This bit determines whether the device supports full-

duplex or half-duplex. A ‘1’ indicates full-duplex operation and a ‘0’

indicates half-duplex. This bit will default to ‘0’ upon reset and will

be writeable if the TECH[2:0] pins are all logic zero and auto-

negotiation is not enabled. If auto-negotiation is not enabled and

the TECH[2:0] pins are set to indicate that only full-duplex is

supported, this bit will be forced to ‘1’ and will not be writeable. If

auto-negotiation is not enabled and the TECH[2:0] pins are set to

indicate that only half-duplex is supported, this bit will be forced to

‘0’ and will not be writeable. When auto-negotiation is enabled, this

bit will not be writeable and will have no effect on the device. If the

TECH[2:0] pins are brought to zero from another value, this bit will

retain its original value until it is overwritten.

0.7 COLT R/W 0

Collision Test: When this bit is set to ‘1’, the device will assert the

COL signal in response to the assertion of the TX_EN signal.

Collision test is disabled if the PCSBP pin is high. Collision test can

be activated regardless of the duplex mode of operation.

0.6:0 RSVD R 0

Reserved

MR1: Status Register

Bits 1.15 through 1.11 reflect the ability of the 78Q2120C as configured by the TECH[2:0] pins. They do not

reflect any ability changes made via the MII Management interface to bits 0.13 (SPEEDSL) , 0.12 (ANEGEN) and

0.8 (DUPLEX).

BIT SYMBOL TYPE DEFAULT DESCRIPTION

1.15 100T4 R 0 100BASE-T4 Ability: Reads ‘0’ to indicate the 78Q2120C does not

support 100Base-T4 mode.

1.14 100X_F R (1) 100BASE-TX Full Duplex Ability:

0 : Not able

1 : Able

1.13 100X_H R (1) 100BASE-TX Half Duplex Ability:

0 : Not able

1 : Able

1.12 10T_F R (1) 10BASE-T Full Duplex Ability:

0 : Not able

1 : Able

1.11 10T_H R (1) 10BASE-T Half Duplex Ability:

0 : Not able

1 : Able

1.10 100T2_F R 0 100BASE-T2 Full Duplex Ability: Reads ‘0’ to indicate the

78Q2120C does not support 100Base-T2 full duplex mode.