33784 Datasheet, PDF (18/30 Pages) Freescale Semiconductor, Inc – DSI 2.02 Sensor Interface

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.
Data
Address
Command
– BSH BSL OD PA3 PA2 PA1 PA0 A3 A2 A1 A0 0 0 0 0
Not Valid
Not Valid
Word Type
LW
SW & ESW (8-bit)
ESW (10-bit)
Response
Word Type
A3 A2 A1 A0 0 0 0 0 0 BSH BSL 0 PA3 PA2 PA1 PA0
LW
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
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.
33784
18
Analog Integrated Circuit Device Data
Freescale Semiconductor