USB2517 datasheet(41/58 Pages) MICROCHIP

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 2013-2016 Microchip Technology Inc.

DS00001598B-page 41

USB2517/USB2517I

7.3.4

SLAVE DEVICE TIME-OUT

According to the SMBus Specification, V1.0 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).

7.3.5

STRETCHING THE SCLK SIGNAL

The Hub supports stretching of the SCLK by other devices on the SMBus. The Hub does not stretch the SCLK.

7.3.6

SMBUS TIMING

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

Diagram” section.

7.3.7

BUS RESET SEQUENCE

The SMBus Slave Interface resets and returns to the idle state upon a START field followed immediately by a STOP

field.

7.3.8

SMBUS ALERT RESPONSE ADDRESS

The SMBALERT# signal is not supported by the Hub.

7.3.8.1

Undefined Registers

The registers shown in Table 7-1 are the defined registers in the Hub. Reads to undefined registers return to 00h. Writes

to undefined registers have no effect and do not return an error.

7.3.8.2

Reserved Registers

Unless otherwise instructed, only a ‘0’ may be written to all reserved registers or bits.

7.4

Default Configuration Option

The MCHP Hub can be configured via its internal default configuration. (Please see Section 7.2.1, "Internal Register Set

(Common to EEPROM and SMBus)" for specific details on how to enable default configuration.)

Please refer to Table 7-1 for the internal default values that are loaded when this option is selected.

7.5

Default Strapping Options:

The USB2517/USB2517I can be configured via a combination of internal default values and pin strap options. Please

see Table 5-1, "USB2517/USB2517I Pin Descriptions" and Table 5-2, "USB2517I SMBUS or EEPROM Interface

Behavior" for specific details on how to enable the default/pin-strap configuration option.

The strapping option pins only cover a limited sub-set of the configuration options. The internal default values will be

used for the bits & registers that are not controlled by a strapping option pin. Please refer to Table 7-1 for the internal

default values that are loaded when this option is selected.

The Amber and Green LED pins are sampled after RESET_N negation, and the logic values are used to configure the

hub if the internal default configuration mode is selected. The implementation shown below (see Section 7.6, "Reset")

shows a recommended passive scheme. When a pin is configured with a “Strap High” configuration, the LED functions

with active low signalling, and the PAD will “sink” the current from the external supply. When a pin is configured with a

“Strap Low” configuration, the LED functions with active high signalling, and the PAD will “source” the current to the

external LED.

Note:

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

communications port after a start or stop condition. The Slave Device Time-Out must be implemented.

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