EMC6D103 datasheet(21/89 Pages) SMSC

21 / 89 page

Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features

Datasheet

SMSC EMC6D103

Revision 0.4 (04-04-05)

DATASHEET

According to SMBus specification, v2.0 devices in a transfer can abort the transfer in progress and

release the bus when any single clock low interval exceeds 25ms (TTIMEOUT, MIN). Devices that have

detected this condition must reset their communication and be able to receive a new START condition

no later than 35ms (TTIMEOUT, MAX).

Note: Some simple devices do not contain a clock low drive circuit; this simple kind of device typically

may reset its communications port after a start or stop condition

5.7

Stretching the SCLK Signal

The EMC6D103 supports stretching of the SCLK by other devices on the SMBus. The Hardware

Monitor Block does not stretch the SCLK.

5.8

SMBus Timing

The SMBus Slave Interface complies with the SMBus AC Timing Specification. See the SMBus timing

diagram shown in the section titled Section 9.2, "SMBus Interface," on page 84.

5.9

Bus Reset Sequence

The SMBus Slave Interface will reset and return to the idle state upon a START field followed

immediately by a STOP field.

5.10

SMBus Alert Response Address

The EMC6D103 device responds to the SMBus Alert Response Address, 0001 100, if the INTEN bit

(register 7Ch bit 2) is set and one or more status events bits are high. The interrupt signal (INT#),

which can be enabled on either the PWM2 or TACH3 pins, can be used as the SMBALERT#. See the

section describing the Interrupt Status Registers on page 26 and the section describing the Interrupt

Pin on page 28 for more details on interrupts.

The device can signal the host that it wants to talk by pulling the SMBALERT# low, if a status bit is

set in one of the interrupt status registers and properly enabled onto the INT# pin. The host processes

the interrupt and simultaneously accesses all SMBALERT# devices through a modified Receive Byte

operation with the Alert Response Address (ARA).

The EMC6D103 device, which pulled SMBALERT# low, will acknowledge the Alert Response Address

and respond with its device address. The 7-bit device address provided by the EMC6D103 device is

placed in the 7 most significant bits of the byte. The eighth bit can be a zero or one.

After acknowledging the slave address, the EMC6D103 device will disengage the SMBALERT# pull-

down by clearing the INT enable bit. If the condition that caused the interrupt remains, the Fan Control

device will reassert the SMBALERT# on the next monitoring cycle, provided the INT enable bit has

been set back to ‘1’ by software.

Note: The INT# signal is an alternate function on the PWM2 and TACH3 pins. The EMC6D103 device

will respond to the SMBus Alert Response address even if the INT# signal is not selected as

the alternate function on one of these pins as long as the following conditions exist: the INTEN

Table 5.4 Modified SMBus Receive Byte Protocol Response to ARA

FIELD:

START

ALERT

RESPONSE

ADDRESS

ACK

EMC6D103 SLAVE

ADDRESS

NACK

STOP

Bits:

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