AM79C930VCW datasheet(123/161 Pages) AMD

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Am79C930

then a 16-bit deep serial FIFO is inserted into the TX data path. This

FIFO allows for some mismatch to be tolerated in the clock rates

between the Am79C930 internal transmit clock and the external

TXC clock that is connected to the TXC input. Because of this inter-

nal FIFO, the appearance of transmit data from the setting of the

TXS bit in TIR8 will be delayed by 8 bit times whenever the TXCIN

bit has the value of 1.

The control of the function of the TXC pin is described in the

Multi-

Function Pin section.

2:0

DR[2:0]

001b

Data Rate. The value in this register determines the data rate for the

network. The TXC output pin will be affected. The following inter-

pretations have been assigned to these bits:

DR[2:0]

CLKGT20

Network

TCR30[2:0]

MIR9[7]

Data Rate

000

reserved

001

fCLKIN

÷20

010

fCLKIN

÷40

011

fCLKIN

÷80

100

reserved

101

fCLKIN

÷200

110

fCLKIN

÷2000

111

reserved

000

fCLKIN

÷20

001

fCLKIN

÷40

010

fCLKIN

÷80

011

fCLKIN

÷160

100

reserved

101

fCLKIN

÷400

110

fCLKIN

÷4000

111

reserved

The Data Rate bits are used together with the CLKGT20 bit to con-

trol clock divider circuits in the DPLL section of the TAI and in the

Transmit State machine section of the TAI. Specifically, the DPLL

clock source will always be set at a rate of 20 times the desired Net-

work Data rate in order to provide the appropriate amount of over-

sampling to insure proper DPLL tracking of the incoming signal.

The Transmit State machine section of the TAI logic will receive a

divided clock that is equal to the desired Network Data Rate.

Note that if the CLKIN frequency is greater than 20 MHz, then the

CLKGT20 bit must be set to 1.

TCR31: Device Revision

This register is the Device Revision register.

CONFIGURATION REGISTER INDEX:

1Fh

Bit

Name

Reset Value

Description

7–0

REV[7:0]

01h

Revision Number. The value in this field contains the revision num-

ber for the current device. The lowest revision number is 01h.

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