TNETX15VE datasheet(70/113 Pages) TI1

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TNETX15VE

VLAN-ENGINE ADDRESS-LOOKUP DEVICE

SPWS028B – APRIL 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

host (access) register space

The TNETX15VE registers, SRAM (internal and external), and EEPROM are indirectly accessed through the

access registers. The access registers are written/read to/through the DIO interface. There are four byte-wide

access registers. They are individually selected through the SAD bus, as shown in the following, and the

registers are read/written through the SDATA bus.

SAD1

SAD0

ACCESS REGISTERS

DIO address low

DIO address high

DIO data

DIO data auto-increment

Two bytes, DIO address low and DIO address high, are used to select the address (DIOADR) of the internal

least-significant byte. The DIO address register is byte writeable. The user does not have to write to both DIO

address locations for each access to the internal registers. This saves time in register accesses. Up to 216

possible locations can be accessed through the DIO address register.

A special function (incorporated into this interface) is a hardware reset that is given to the TNETX15VE through

the use of the host registers. A hard reset is achieved by writing 0x40 to DIO address high. The value in DIO

address low is don’t care. Writing this code is equivalent to electrically setting the RESET terminal to 0.

The next two bytes, DIO data and DIO data auto-increment, are used to read and write data to the byte-wide

internal register selected in the DIOADR. Both DIO data and DIO data auto-increment can be effectively used

to read and write the data, but the DIO data auto-increment register provides additional functionality over DIO

data. Access to the DIO data auto-increment register provides a post-increment (by one) to the DIO address

As an example, to access a single-byte-wide register such as the SIO register (DIO address = 0x0A) the

operations needed are:

• Write a 0x00 to DIO address high

• Write a 0x0A to DIO address low to select DIO address 0x0A

• Read the SIO register by reading DIO data, or write to the SIO register by writing to DIO data.

Multiple-byte registers are accessed by reading/writing to their individual bytes. The control register (DIO

address 0x08–0x09) is accessed in the following manner:

• Write a 0x00 to DIO address high

• Write a 0x08 to DIO address low to select DIO address 0x08

• Read the least-significant bit of the control register by reading DIO data, or write to the least-significant

bit of the control register by writing to DIO data.

• Write a 0x00 to DIO address high

• Write a 0x09 to DIO address low to select DIO address 0x09

• Read the most-significant bit of the control register by reading DIO data, or write to the most-significant

bit of the control register by writing to DIO data.

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