MC33789 Datasheet, PDF (63/80 Pages) Freescale Semiconductor, Inc – Airbag System Basis Chip (SBC) with Power Supply and PSI5 Sensor Interface

FUNCTIONAL DEVICE OPERATION
SENSOR MESSAGE, OPERATION COMMAND AND SPI
There are two status bits latched in the 33789 after they
are set to their 'active' states. Once the bits are read via a
STATUS command, they are set to their 'inactive' states.
Only an internal reset and the STATUS read command can
set these bits to their 'inactive' states, and immediately after
either of them occur, the states are updated to reflect their
true status. This is designed to ensure intermittent error
conditions can be detected by the system.
The following table defines these bits and their 'active' and
'inactive' states:
Table 30. Two Latched Status
Bit Name
Function
Active State
BOT
Boost Supply Over-
temperature
1
IGN
IGNSTAT state
0
Inactive State
0
1
The WDR bit is set whenever the 33789 detects an
incorrect watchdog refresh, and can be cleared by a WSM
Reset or by a correct watchdog feed.
Table 31. SPI Command - STATUS
STATUS(0x56, 0x96)
Write *
15 14 13 12 11 10 9 8
7
SI
01010110
X
SO
000P1110
0
6
5
4
3
2
1
0
X
X
X
X
X
X
X
0
0
0
0
0
1
0
Read
SI
10010110
X
X
X
X
X
X
X
X
SO
0
1
0
P
1
1
1
0 SOT DCOT BOT IGN
WU
WS1 WS0 WDR
Default →
Default →
Default →
Default →
Default →
Default →
SOT
0
1
Sync Supply Over-temperature Error
Sync supply over-temperature error not detected
Sync supply over-temperature error detected
DCOT
0
1
DC Sensor Regulator Over-temperature Error
DC sensor regulator over-temperature error not detected
DC sensor regulator over-temperature error detected
BOT
0
1
Boost Supply Over-temperature Error
Boost supply over-temperature error not detected
Boost supply over-temperature error detected
IGN
0
V_PWR < IGNSTAT threshold V_{BST_UV}
1
V_PWR ≥ IGNSTAT threshold V_{BST_UV}
WU
0
WAKE Pin = 0
1
WAKE Pin = 1
IGNSTAT State
Wake Pin State
WS1
0
0
1
1
WS0
0
1
0
1
Watchdog State
Function
Watchdog State = “INITIAL”
Watchdog State = “DRIVE” and ARM_LOCKOUT = 0
Watchdog State = “DRIVE” and ARM_LOCKOUT = 1
Watchdog State = “WDOG_TEST” or “WDOG_OVERRIDE”
WDR
Watchdog Error Status
Analog Integrated Circuit Device Data
Freescale Semiconductor
33789
63