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LXT9883/9863 — Advanced 10/100 Unmanaged Repeater

Datasheet

Document #: 249115

Revision #: 003

Rev. Date: 08/07/01

4.2.9.3

Serial LEDs

The LXT98x3 provides a serial interface to support additional LED options. Standard shift

registers, either 74X595s (8-bit Serial-to-Parallel with Output Registers) or 74X164s (8-bit S/P

without registers) can be used to drive these additional LEDs. Collision10/100 and Activity10/100

status indications are provided on multiplexed configuration pins and duplicated on the serial port.

The LED serial interface consists of three outputs: clock (LEDCLK), parallel latch clock

(LEDLAT), and output data (LEDDAT). The parallel latch clock is used only with the 74X595

implementation. Refer to Figure 14 for an illustration of the LED serial interface circuit.

Potentially, 30 LEDs can be driven by the LED serial interface via 4 S/P devices. The S/P serial

output is connected to the serial input of the first serial input device. To expand the chain, connect

the last serial output to serial input of next serial interface device.

Serial LED data is output in the anticipated priority order, from least likely to most likely to be

used:

• Unused ‘595/‘164 parallel outputs

• MII Ports - LED1, 2, 3

• Miscellaneous LEDs (Repeat of Collision10/100, Repeat of Activity10/100, Global Fault,

RPS Fault)

• ACTGLED10

• ACTGLED100

This allows the user to leave off devices in the serial-to-parallel chain if the LEDs associated with

that condition aren’t desired. Refer to Figure 6 on page 23 which illustrates the LED serial interface

port signalling and Table 8 on page 23 which documents the Serial LED Stream.

Figure 14. Serial LED Circuit

SER

RCLK

SRCLK

Qh‘

LED cct.

VLED

LED cct.

VLED side

VLED = 3.3 to 5 Volts +/- 5%

74X595

LED cct.

Up to 2 more

‘595s/8xLEDs

LEDDAT

LEDLAT

LEDCLK

Up to 2 more

‘164s/8xLEDs

LED cct.

VLED

LED cct.

LEDDAT

LEDCLK

CLK

74X164

CLK

74X164

SER

RCLK

SRCLK

Qh‘

74X595

LXT98x3

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