DS125RT410 Datasheet, PDF (16/42 Pages) Texas Instruments – DS125RT410 Low Power Multi-Rate Quad Channel Retimer

DS125RT410
SNLS459 – APRIL 2011
DEVICE CONFIGURATION MODES
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The DS125RT410 can be configured using two different methods.
• SMBus Master Configuration Mode
• SMBus Slave Configuration Mode
The configuration mode is selected by the state of the SMBus Enable pin (pin 20) when the DS125RT410 is
powered-up. This pin should be either left floating or tied to the device V_DD through an optional 1KΩ resistor. The
effect of each of these settings is shown in Table 3.
Pin Setting
Float
High (1)
Table 3. SMBus Enable Settings
Configuration Mode
SMBus Master Mode
SMBus Slave Mode
Description
READ_EN Pin
Device reads its configuration
from an external EEPROM on
power-up.
Pull low to initiate reading
configuration data from external
EEPROM
Device is configured over the
Tie low to enable proper address
SMBus by an external controller. strapping on power-up
SMBus Master Mode and SMBus Slave Mode
In SMBus master mode the DS125RT410 reads its initial configuration from an external EEPROM upon power-
up. A description of the operation of this mode appears in a separate application note.
Some of the pins of the DS125RT410 perform the same functions in SMBus master and SMBus slave mode.
Once the DS125RT410 has finished reading its initial configuration from the external EEPROM in SMBus master
mode it reverts to SMBus slave mode and can be further configured by an external controller over the SMBus.
There are two pins that provide unique functions in SMBus master mode. These are as follows:
• ALL_DONE
• READ_EN
These pins are meant to work together. When the DS125RT410 is powered up in SMBus master mode, it reads
its configuration from the external EEPROM when the READ_EN pin goes low. When the DS125RT410 is
finished reading its configuration from the external EEPROM, it drives its ALL_DONE pin low. After the
DS100RT410 has finished reading its configuration from the EEPROM, it releases control of the SMBus and
becomes a SMBus slave. In applications where there is more than one DS125RT410 on the same SMBus, bus
contention can result if more than one DS125RT410 tries to take command of the SMBus at the same time. The
READ_EN and ALL_DONE pins prevent this bus contention.
The system should be designed so that the READ_EN pin of one of the DS125RT410s in the system is driven
low on power-up. This DS125RT410 will take command of the SMBus on power-up and will read its initial
configuration from the external EEPROM. When it is finished reading its configuration, it will set its ALL_DONE
pin low. This pin should be connected to the READ_EN pin of another DS125RT410. When this DS125RT410
senses its READ_EN pin driven low, it will take command of the SMBus and read its initial configuration from the
external EEPROM, after which it will set its ALL_DONE pin low. By connecting the ALL_DONE pin of each
DS125RT410 to the READ_EN pin of the next DS125RT410, each DS125RT410 can read its initial configuration
from the EEPROM without causing bus contention.
For SMBus slave mode, the READ_EN pin must be tied low. Do not leave it floating or tie it high.
A connection diagram showing several DS125RT410s along with an external EEPROM and an external SMBus
master is shown in Figure 3 below. The SMBus master must be prevented from trying to take control of the
SMBus until the DS125RT410s have finished reading their initial configurations from the EEPROM.
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