33784 datasheet(18/30 Pages) FREESCALE

18 / 30 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33784

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

Normally enhanced long responses will be sent for

enhanced long commands, and enhanced short responses

will be sent for enhanced short commands of the same

length. If an enhanced long word is sent after an enhanced

short word, or an enhanced short word is sent after an

enhanced long word, or two enhanced short words of

different lengths are sent in succession, then the first

response will have a different length than the second

command, and therefore the first response will be invalid.

LOGIC COMMANDS AND REGISTERS

INTRODUCTION

The following sections describe in detail each of the

commands that can be sent to the 33784. All of these

commands can be sent in long-word format (standard or

enhanced). Some of the commands can be sent in short-

word format (standard or enhanced), but not all. Refer to the

table in each section for the available formats for each

command. The responses for each command can also be

found in the tables. The 4-bit CRC, which is appended to

every command and every response, has been omitted.

Many commands have “don't-care” bits, which can be set

to 0 or 1 without affecting the command. Although the 33784

will respond the same in either case, it is recommended that

all “don't-care” bits be set to 0 to maintain future compatibility.

INITIALIZATION COMMAND AND RESPONSE

(BUSIN INPUT ONLY)

Following power-up or after a POR has occurred, the

Initialization Command must be sent to the 33784 before it

will respond to other commands. The command format is

found in Figure 9.

The Initialization Command may be used to initialize a

daisy chain device. The Initialization Command is sent to

address zero. The command will be received by the next

daisy chain device with its bus switch open. Reception of this

command will assign the device address and close the bus

switch if the BSH and BSL bits are logic [1]

Once a device has received an Initialization Command, it

will ignore further initialization commands unless it has

received a clear command or undergone a power-ON reset.

The response is sent during the next message following a

valid Initialization Command to the addressed device. The

response is shown in Figure 9. Because this is a long-word

only command, there is no short word response. The BSH

and BSL bits returned are the same as the bits sent in the

command. The Request Status command can be used to find

the logic commanded state of the bus switches.

Figure 9. Initialization Command Response Format

REQUEST STATUS COMMAND AND RESPONSE

This command causes the addressed device to return the

status of the BSH and BSL bits and the logic levels of the I/

O. The command format is found in Figure 10.

The 33784 will only act on this 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.

Data

Address

Command

Word Type

–

BSH BSL

PA3 PA2 PA1 PA0

Not Valid

SW & ESW (8-bit)

Not Valid

ESW (10-bit)

Response

Word Type

BSH BSL

PA3 PA2 PA1 PA0

No Response

SW & ESW (8-bit)

No Response

ESW (10-bit)

Legend

A[3:0] = Address bits. The slave address.

An address value of 0000 is ignored by all devices (no

initialization, no bus switch closure, and no response)

BSH = High Side Bus Switch Position (1 = closed).

BSL = Low Side Bus Switch Position (1 = closed).

“–” = Don’t care bit. Can be 0 or 1.

PA[3:0] = Bus address to set the device to.

An address value of 0000 is ignored by all devices (no

initialization, no bus switch closure, and no response)

OD = Oscillator dither:

0 = no dither (default)

1 = dither

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