33784 datasheet(23/30 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33784

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

CLEAR COMMAND AND RESPONSE

This command will open the bus switch and reset all

registers to the reset state. The command format is found in

Figure 16. No response is generated for the clear command.

The 33784 will only act on this command if the address bits

in the command match the address that the device was

initialized with, or if the address bits are 0000.

Figure 16. Clear Command Format and Response Format

FORMAT CONTROL COMMAND AND RESPONSE

This command allows the short-word length, the CRC

polynomial, and the CRC seed to be changed. It is also the

command needed to switch the device from the “standard”

mode to the “enhanced” mode.

The response is sent during the next message following a

valid Format Control command to the addressed device.

Because this is a long-word only command, there is no short

word response.

On power-up or following a “Clear” command, the device

uses the standard DSI short-word length (8 data bits) and

standard CRC polynomial (x4 + 1) and seed (1010).

The registers associated with Format Control default to

values that correspond to Standard DBUS operation upon

power-up, or at the issuance of a “Clear” command.

Changes made to the Format Control Register do not

become active until the 4 bits of the format selection register

are set during a single write command. It will not switch back

to Standard DBUS settings unless all 4 bits of the format

selection register are cleared by a single write.

Any attempts to change the format will be ignored while in

the enhanced mode.

The Format Control command is a long-word Command

and contains 8 bits of data which are used to determine read

or write, the specific format control register, and the data to

be written/read. The format for this command is defined in

Figure 17.

If the R/W bit is set, the value in the Data Bits will be written

to the format control register pointed to by the 3-bit format

pointed to by the format register address will not be changed,

but the values in it will be returned in the following response

from the device. No data can be written to the reserved

registers.

The response to this command will be the data that was

written/read by the command. Attempts to write to the

reserved registers will return zeros in the data bits of the

response.

The 33784 will only act on the Format Control Command if

the address bits in the command match the address that the

device was initialized with. If the addresses do not match, the

device will do nothing and no response will be generated. The

only exception is the global address of 0000. If the address

bits in the command are 0000, the 33784 will perform all

normal functions associated with the command, but no

response will be generated.

Data

Address

Command

Word Type

––––––––

0111

LW & ELW

0111

SW & ESW (8-bit)

––

0111

ESW (10-bit)

Response

Word Type

No Response

LW & ELW

No Response

SW & ESW (8-bit)

No Response

ESW (10-bit)

Legend

A[3:0] = Address bits. The address of the selected device.

An address value of 0000 clears all devices.

“–” = Don’t care bit. Can be 0 or 1.

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