AM79C976 datasheet(158/309 Pages) AMD

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Am79C976

8/01/00

P R E L I M INARY

LED0 Control Register

Offset 0E0h

This register controls the function(s) that the LED0 pin

displays. Multiple functions can be simultaneously en-

abled on this LED pin. The LED display will indicate the

logical OR of the enabled functions. This register de-

faults to Link Status (LNKST) with pulse stretcher en-

abled (PSE = 1) and is fully programmable.

All bits in this register are restored to their default val-

ues when the RST pin is asserted, before the serial

EEPROM is read, and after a serial EEPROM read er-

ror.

This register is an alias of BCR4.

Table 63. LED0 Control Register

Bit

Name

Description

LEDOUT

This bit indicates the current (non-stretched) value of the LED output pin. A value of 1 in this bit

indicates that the OR of the enabled signals is true.

The logical value of the LEDOUT status signal is determined by the settings of the individual Status

Enable bits of the LED register (bits 8 and 6-0).

LEDPOL

LED Polarity. When this bit has the value 0, then the LED pin will be driven to a LOW level whenever

the OR of the enabled signals is true, and the LED pin will be disabled and allowed to float high

whenever the OR of the enabled signals is false (i.e., the LED output will be an Open Drain output

and the output value will be the inverse of the LEDOUT status bit).

When this bit has the value 1, then the LED pin will be driven to a HIGH level whenever the OR of

the enabled signals is true, and the LED pin will be driven to a LOW level whenever the OR of the

enabled signals is false (i.e., the LED output will be a Totem Pole output and the output value will

be the same polarity as the LEDOUT status bit.).

The setting of this bit will not effect the polarity of the LEDOUT bit for this register.

The default value of this bit is 0.

LEDDIS

LED Disable. This bit is used to disable the LED output. When LEDDIS has the value 1, then the

LED output will always be disabled. When LEDDIS has the value 0, then the LED output value will

be governed by the LEDOUT and LEDPOL values.

The default value of this bit is 0.

100E

100 Mbps Enable. When this bit is set to 1, a value of 1 is passed to the LEDOUT bit in this register

when the Am79C976 controller is operating in 100 Mbps mode.

The default value of this bit is 0.

11-10

RES

Reserved locations. Written and read as undefined.

MPSE

Magic Packet Status Enable. When this bit is set to 1, a value of 1 is passed to the LEDOUT bit in

this register when Magic Packet frame mode is enabled and a Magic Packet frame is detected on

the network.

The default value of this bit is 0.

8FDLSE

Full-Duplex Link Status Enable. Indicates the Full-Duplex Link Test Status. When this bit is set, a

value of 1 is passed to the LEDOUT signal when the Am79C976 controller is functioning in a Link

Pass state and full-duplex operation is enabled. When the Am79C976 controller is not functioning

in a Link Pass state with full-duplex operation being enabled, a value of 0 is passed to the LEDOUT

signal.

The default value of this bit is 0.

PSE

Pulse Stretcher Enable. When this bit is set, the LED illumination time is extended for each new

occurrence of the enabled function for this LED output. A value of 0 disables the pulse stretcher.

The default value of this bit is 1.

LNKSE

Link Status Enable. When this bit is set, a value of 1 will be passed to the LEDOUT bit in this

The default value of this bit is 1.

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