BeagleBoard XM C2, Reference Manual

Page: 64 / 163

REF: BB_SRM_xM
BeagleBoard-xM System
Reference Manual
Revision C2
Page 64 of 163
Figure 28. Reset Circuitry
7.9.4.1 Warm Reset
The warm reset is generated by the processor on power up. The
nRESWARM signal is a
bidirectional reset. When an internal reset occurs, nRESWARM goes low and resets all
the peripherals and the TPS65950 . The TPS65950 can be configured to perform a warm
reset of the device to bring it into a known defined state by detecting a request for a warm
reset on the
NRESWARM pin. The minimum duration of the pulse on the nRESWARM
pin should be two 32-kHz clock cycles. The nRESWARM output is open-drain;
consequently, an external pullup resistor is required. There is no way for the user to
generate a warm reset on the BeagleBoard.
7.9.4.2 Cold Reset
On power up as shown in
Figure 27 , the TPS65950 generates nRESPWRON , power on
reset. The signal from the TPS65950 is an output only and is not an open drain signal.
By running the signal through a buffer, SN74LVC2G07 , the signal becomes open drain,
which requires a pullup on the signal. This will allow the nRESPWRON signal to be
pulled low, by pressing the reset switch S2 , to force a reset to the PROCESSOR
processor and to any device on the expansion card that require a reset.
It also allows for the reset signal to be pulled low or held low for an extended time by
circuitry on the expansion card if needed.
7.9.4.3 User Reset
The USER RESET button can be used to request a Warm Reset from the processor. After
initialization, this pin becomes an input to the processor. By pushing the Reset button, an
interrupt is generated into the processor. The software that is run as a result of this can
then do whatever housekeeping is required and then send the processor into a reset mode.
P9
2
4
6
8
10
12
14
16
18
20
22
24
26
28
1
3
5
7
9
11
13
15
17
19
21
23
25
27
R61
4.7K VIO_1V8
U5A
SN74LVC2G07DCKR
1
2
5
6
VBAT
IO_1P8
T
P
S
6
5
9
5
0
U7A
B13
A13
A11
nRESWARM
nRESPWRON
PWRON
nRESPWRON
VIO_1V8
R42
10K
C12
0.1uF
VBAT
PWRON
R59 4.7K
S2
B3F-1000
1 3
2 4
R53
DNI
nRESWARM
VIO_1V8
PROCESSOR
U4B DM3730
AH25
AF24
SYS_nRESPWRON
SYS_nRESWARM/GPIO_30
nRESET