1998 Oct 07
57
Philips Semiconductors
Product specification
Pager baseband controller
PCA5007
6.21
Reset
To initialize the PCA5007 a reset is performed by using
either of the 2 following methods:
Applying an external reset signal to the RESETIN pin
Via the on-chip watchdog timer.
The reset state of the output pins is given in separate
tables (Tables 2 to 6). The reset state of the SFRs is given
in a separate overview (see Table 1).
While a reset is applied to the device the output RESOUT
is driven LOW.
The internal RAM is not affected by reset. When V
DD
is
turned on, the RAM contents are indeterminate.
6.21.1
E
XTERNAL RESET USING THE
RESETIN
PIN
The external reset input for the PCA5007 is the RESETIN
pin. A Schmitt trigger is used at the input for noise
rejection. Immediately after pin RESETIN goes HIGH, an
internal reset is executed. As a consequence the SFRs
and port pins adopt their reset state, ALE and PSEN are
held HIGH. As long as the RESETIN pin stays HIGH, the
reset state is maintained. When RESETIN goes LOW, the
device start-up sequence is executed (see Section 6.22).
6.21.2
E
XTERNAL POWER
-
ON RESET USING THE
RESETIN
PIN
An automatic reset can be obtained by connecting the
RESETIN pin to V
BAT
via a capacitor and to V
SS
via a
resistor. At power-on, the voltage on the RESETIN pin is
equal to V
BAT
and decreases from V
BAT
as the capacitor
charges through the resistor to V
SS
. V
RESETIN
must remain
higher than the threshold of the Schmitt trigger for a
duration of t
RESETIN
(see Chapter “AC characteristics”).
The reset configuration is shown in Fig.28.
6.21.3
I
NTERNAL RESET
The watchdog which is available in the PCA5007
(see Section 6.16) will force a reset if it is enabled and
expires.
A reset is also forced, when the DC/DC converter restarts
operation from the off mode (see Section 6.22.3).
All resets to the microcontroller can be observed as
negative pulses at the output RESOUT.
Fig.28 Application diagram for external power-on reset configuration.
handbook, full pagewidth
MGR131
VBAT
VBAT
VSS
RESETIN
RESET AND
POWER
CONTROLLER
internal reset
for microcontroller
RESOUT
PCA5007
watchdog
restart DC/DC
converter
10
μ
F
10 k