FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
The SI/SO pins of the 33874 follow a first-in first-out (D15
SPI PROTOCOL DESCRIPTION
to D0) protocol, with both input and output words transferring
the most significant bit (MSB) first. All inputs are compatible
with 5.0V CMOS logic levels.
The SPI interface has a full duplex, three-wire
synchronous data transfer with four I/O lines associated with
it: Serial Input (SI), Serial Output (SO), Serial Clock (SCLK),
and Chip Select (CS).
CS
CSB
CS
SCLK
SI
D15
D14
D13
D12 D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
SO
OD15 OD14 OD13 OD12 OD11 OD10 OD9 OD8 OD7 OD6 OD5 OD4 OD3 OD2 OD1 OD0
Notes 1. RST is a logic [1] state during the above operation.
2. D15 D0 relate to the most recent ordered entry of data into the device.
:
NOTES: 1. RSTB is in a logic H state during the above operation.
3. OD15:OD0 relate to the first 16 bits of ordered fault and status data out of the device.
device.
2. DO, D1, D2, ... , and D15 relate to the most recent ordered entry of program data into the LUX IC
Figure 9. Single 16-Bit Word SPI Communication
OPERATIONAL MODES
The 33874 has four operating modes: Sleep, Normal,
SLEEP MODE
Fault, and Fail-safe. Table 5 summarizes details contained in
succeeding paragraphs.
The Default mode of the 33874 is the Sleep Mode. This is
the state of the device after first applying battery voltage
(VPWR) prior to any I/O transitions. This is also the state of the
Table 5. Fail-Safe Operation and Transitions to Other
33874 Modes
device when the WAKE and RST are both logic [0]. In the
Sleep Mode, the output and all unused internal circuitry, such
as the internal 5.0V regulator, are off to minimize current
draw. In addition, all SPI-configurable features of the device
are as if set to logic [0]. The 33874 will transition to the
Normal or Fail-safe operating modes based on the WAKE
and RST inputs as defined in Table 5.
Mode
FS Wake RST WDTO
Comments
Sleep
x
0
0
x
Device is in Sleep mode. All
outputs are OFF
Normal
Fault
1
x
1
No
No
Normal mode. Watchdog is
active if enabled.
0
0
0
1
1
1
1
1
0
0
1
1
1
0
1
1
1
0
Device is currently in fault
mode. The faulted output(s)
is (are) OFF.
NORMAL MODE
The 33874 is in Normal Mode when:
• VPWR and VDD are within the normal voltage range.
Watchdog has timed out and
the device is in Fail-safe
Mode. The outputs are as
configured with the RFS
resistor connected to FSI.
RST and WAKE must go
from logic [1] to logic [0]
simultaneously to bring the
device out of the Fail-safe
mode or momentarilytied the
FSI pin to ground.
•
RST pin is logic [1].
• No fault has occurred.
Fail-
Safe
Yes
FAIL-SAFE MODE
FAIL-SAFE MODE AND WATCHDOG
If the FSI input is not grounded, the watchdog timeout
detection is active when either the WAKE or RST input pin
transitions from logic [0] to logic [1]. The WAKE input is
capable of being pulled up to VPWR with a series of limiting
x = Don’t care.
33874
Analog Integrated Circuit Device Data
Freescale Semiconductor
18
FREESCALE [ Freescale ]
