33784 datasheet(13/30 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33784

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

BUS SWITCHES

A high side bus switch lies between BUSIN and BUSOUT

and a low side bus switch lies between RTNIN and RTNOUT.

These switches can be opened or closed via commands on

the bus. The bus switch facilitates the daisy chain operation

of the 33784. When the switch is open, BUSIN is isolated

from BUSOUT, RTNIN is isolated from RTNOUT, and any

communication that is seen on one pin will not be transmitted

to the other. In this way, the CCU can initialize the first 33784

or any other slave device in the daisy chain and program an

address into it.

Once the first device in the daisy chain is initialized, the

bus switches can be closed, effectively shorting BUSIN to

BUSOUT, and RTNIN to RTNOUT. Now all communication

that is seen on one pin will be passed to the other. The Master

IC can send a command through the initialized device to the

next un-initialized device in the daisy chain. The process is

repeated until every device in the daisy chain has been

initialized with a unique address.

Once a device’ bus switches are closed they remain

closed except for the following conditions:

- reception of a CLEAR command

- bus lines remain below the frame threshold for longer

than the bus timeout period in which case the device will reset

and the bus switches will open.

- HCAP or VREG decay below the POR threshold for a time

exceeding the POR Mask time in which case the device will

reset and the bus switches will open.

Once the bus switches open they can only be closed again

with an initialization command.

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