1997 Jun 24
29
Philips Semiconductors
Product specification
Advanced POCSAG Paging Decoder
PCD5003
8
OPERATING INSTRUCTIONS
8.1
Reset conditions
When the PCD5003 is reset by applying a HIGH-level on
input RST, the condition of the decoder is as follows:
OFF status (irrespective of DON input level)
REF output frequency 32768 Hz
All internal counters reset
Status/control register reset
INT output at LOW-level
No alert transducers selected
LED, VIB and ATH outputs at LOW level
ATL output high impedance
SDA, SCL inputs high impedance
Voltage converter disabled.
Within t
RSU
after release of the reset condition (RST LOW)
the programmed functions are activated. The settings
affecting the external operation of the PCD5003 are as
follows:
REF output frequency
Voltage converter
INT output polarity
Signal test mode.
When input DON is HIGH, the decoder starts operating in
ON status immediately following t
RSU
.
8.2
Power-on reset circuit
During power-up of the PCD5003 a HIGH level of
minimum duration t
RST
= 50
μ
s must be applied to pin
RST. This is to prevent EEPROM corruption which might
otherwise occur because of the undefined contents of the
Control register.
The reset signal can be applied by the external
microcontroller or by an RC power-on reset circuit on pin
RST (C to V
PR
, R to V
SS
). Such an RC-circuit should have
a time constant of at least 3t
RST
= 150
μ
s.
Input RST has an internal high-ohmic pull-down resistor
(nominal 2 M
at 2.5 V supply) which could be used
together with a suitable external capacitor connected to
V
PR
to create a power-on reset signal. However, since this
pull-down resistor varies considerably with processing and
supply voltage, the resulting time constant is inaccurate.
A more accurate reset duration can be realised with an
additional external resistor connected to V
SS
.
Recommended minimum values in this case are
C = 2.2 nF and R = 100 k
(see Fig.15).
8.3
Reset timing
The start-up time for the crystal oscillator may exceed
1 second (typ. 800 ms). It is advised to apply a reset
condition at least during the first part of this period.
The minimum reset pulse duration t
RST
is 50
μ
s.
During reset the oscillator is active, but clock signals are
inhibited internally. Once the reset condition is released
the end of the oscillator start-up period can be detected by
a rising edge on output INT.
During a reset the voltage converter clock (V
clk
) is held at
zero. The resulting output voltage drop may cause
problems when the external resetting device is powered by
the internal voltage doubler. A sufficiently large buffer
capacitor between output V
PO
and V
SS
must be provided
to supply the microcontroller during reset. The voltage at
V
PO
will not drop below V
DD
0.7 V.
Immediately after a reset all programmable internal
functions will start operating according to a programmed
value of 0. During the first 8 full clock cycles (t
RSU
) all
programmed values are loaded from EEPROM.
After reset the receiver outputs RXE and ROE become
active immediately, if DON is HIGH and the synthesizer is
disabled. When the synthesizer is enabled, RXE and ROE
will only become active after the second pulse on ZLE
completes the loading of synthesizer data.
The full reset timing is shown in Fig.11. The start-up timing
including synthesizer programming is given in Fig.12.
8.4
Initial programming
A newly-delivered PCD5002 has EEPROM contents which
are undefined. The EEPROM should therefore be
programmed, followed by a reset to activate the SPF
settings, before any attempt is made to use the device.