PCI7621 datasheet(59/298 Pages) TI

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3−3

3.4.2

Device Resets

The following are the requirements for proper reset of the PCI7x21/PCI7x11 controller:

GRST and PRST must both be asserted at power on.

GRST must be asserted for at least 2 ms at power on

PRST must be deasserted either at the same time or after GRST is asserted

PCLK must be stable for 100

µs before PRST is deasserted.

VCC

GRST

PRST

PCLK

> 2 ms

> 0 ns

> 100

Figure 3−3. PCI Reset Requirement

3.4.3

Serial EEPROM I2C Bus

The PCI7x21/PCI7x11 controller offers many choices for modes of operation, and these choices are selected by

programming several configuration registers. For system board applications, these registers are normally

programmed through the BIOS routine. For add-in card and docking-station/port-replicator applications, the

PCI7x21/PCI7x11 controller provides a two-wire inter-integrated circuit (IIC or I2C) serial bus for use with an external

serial EEPROM.

The PCI7x21/PCI7x11 controller is always the bus master, and the EEPROM is always the slave. Either device can

drive the bus low, but neither device drives the bus high. The high level is achieved through the use of pullup resistors

on the SCL and SDA signal lines. The PCI7x21/PCI7x11 controller is always the source of the clock signal, SCL.

System designers who wish to load register values with a serial EEPROM must use pullup resistors on the SCL and

SDA terminals. If the PCI7x21/PCI7x11 controller detects a logic-high level on the SCL terminal at the end of GRST,

then it initiates incremental reads from the external EEPROM. Any size serial EEPROM up to the I2C limit of 16 Kbits

can be used, but only the first 96 bytes (from offset 00h to offset 5Fh) are required to configure the PCI7x21/PCI7x11

controller. Figure 3−3 shows a serial EEPROM application.

In addition to loading configuration data from an EEPROM, the PCI7x21/PCI7x11 I2C bus can be used to read and

write from other I2C serial devices. A system designer can control the I2C bus, using the PCI7x21/PCI7x11 controller

PCI7621 Datasheet(PDF) 59 Page - Texas Instruments