USB2524 datasheet(15/58 Pages) MICROCHIP

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DS00001588B-page 15

USB2524

6.1.2

PERIPHERAL MODE: LEVEL TRIGGERED

In Peripheral Mode (Level Triggered), each pin directly switches a downstream port between the two upstream host

ports. Each pin on the PRT_ASSIGN interface is only capable of two electrical states (either logic low or logic high). The

interface will control downstream port assignment as follows.

PRT_ASSIGN0 = '0', then Port 1 assigned to host 1

PRT_ASSIGN0 = '1', then Port 1 assigned to host 2

PRT_ASSIGN1 = '0', then Port 2 assigned to host 1

PRT_ASSIGN1 = '1', then Port 2 assigned to host 2

PRT_ASSIGN2 = '0', then Port 3 assigned to host 1

PRT_ASSIGN2 = '1', then Port 3 assigned to host 2

PRT_ASSIGN3 = '0', then Port 4 assigned to host 1

PRT_ASSIGN3 = '1', then Port 4 assigned to host 2

6.1.3

PERIPHERAL MODE: EDGE TRIGGERED

Each pin will respond to a positive edge transition that is part of a positive pulse that has a minimum pulse width of

100ns, and will not respond to another positive edge until after a negative pulse with minimum pulse width (that is deter-

mined by the Register D0h: Port Interface Delay Timer (Reset = 0x00) on page 26) has been detected. The combination

of a 100ns positive pulse width and a programmable length negative width requirement provides an effective glitch filter

mechanism for a variety of mechanical switches.

Each positive edge transition will change the upstream host ownership of downstream ports as follows (1st transition

will increment ownership from Host 1 to Host 2, the 2nd transition will increment ownership from Host 2 to Unassigned

(or Host 1, if not using the Unassigned state), and the 3rd transition will increment ownership from Unassigned to Host

1 (note: this “3rd” state will not occur if “unassigned” is not used). Each subsequent transition will continue to increment

the port ownership and will cycle through in similar fashion.

6.2

SMBus Host Control of Port Assignment

In this mode, the SMBus interface remains “live” during operation of the switching hub and is used to switch/assign ports

“on-the-fly” through SMBus commands. This is accomplished through register direct writes to the Port Assignment reg-

isters (see the USB_ATTACH description under Register FFh: Status/Command (Reset = 0x00) on page 35).

Note:

There is a switching delay determined by the Register D0h: Port Interface Delay Timer.

Note:

Power-On default for edge triggered operation is: all ports assigned to Host 1.

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