TUSB2046A

4-PORT HUB FOR THE UNIVERSAL SERIAL BUS

WITH OPTIONAL SERIAL EEPROM INTERFACE

SLLS404 – DECEMBER 1999

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

programming the EEPROM

An SGS Thompson M93C46 EEPROM or equivalent is used for storing the programmable VID and PID. When

the EEPROM interface is enabled (EXTMEM = 0), the EECLK and EEDATA are internally pulled down (100

µA)

inside the TUSB2046A. The internal pulldowns are disabled when the EEPROM interface is disabled (EXTMEM

= 1).

The EEPROM is programmed with the three 16-bit locations as shown in Table 1. Connecting pin 6 of the

EEPROM high (ORG = 1) organizes the EEPROM memory into 64

×16 bit words.

Table 1. EEPROM Memory Map

ADDRESS

D15

D14

D13

D12–D8

D7–D0

00000

0

GANGED

00000

00000

00000000

00001

VID High-byte

VID Low-byte

00010

PID High-byte

PID Low-byte

XXXXXXXX

The D and Q signals of the EEPROM must be tied together using a 1-k

Ω resistor with the common I/O operations

forming a single-wire bus. After system power-on reset, the TUSB2046A performs a one-time access read

operation from the EEPROM if the EXTMEM pin is pulled low and the chip select(s) of the EEPROM is

connected to the system power-on reset. Initially, the EEDATA pin will be driven by the TUSB2046A to send a

start bit (1) which is followed by the read instruction (10) and the starting-word address (00000). Once the read

instruction is received, the instruction and address are decoded by the EEPROM, which then sends the data

to the output shift register. At this point, the hub stops driving the EEDATA pin and the EEPROM starts driving.

A dummy (0) bit is then output and the first three 16-bit words in the EEPROM are output with the most significant

bit (MSB) first.

The output data changes are triggered by the rising edge of the clock provided by the TUSB2046A on the EECLK

pin. The

SGS-Thompson M936C46 EEPROM is recommended because it advances to the next memory

location by automatically incrementing the address internally. Any EEPROM used must have the automatic

internal address advance function. After reading the three words of data from the EEPROM, the TUSB2046A

puts the EEPROM interface into a high-impedance condition (pulled down internally) to allow other logic to share

the EEPROM. The EEPROM read operation is summarized in Figure 8. For more details on EEPROM

operation, refer to

SGS-Thompson Microelectronics M93C46 Serial Microwire Bus EEPROM data sheet.