PCA84C122A PHILIPS [NXP Semiconductors], PCA84C122A Datasheet - Page 11

• Manufacturer Part Number: PCA84C122A
• Description: 8-bit microcontrollers for remote control transmitters
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
8.3
First the ON-time and OFF-time registers are loaded. The
number of pulses to be generated is stored in the Pulse
Counter. The Hardware Modulator starts as soon as the
Pulse Counter is loaded. First the signal OUT is activated
and the ON-time value is stored in the Pulse Timer. Then
the Pulse Timer is counted down with pulses of 1/f
When the Pulse Timer reaches zero the OUT signal
becomes inactive and the value held in the Pulse Counter
is decreased by ‘1’. If the Pulse Counter is not yet zero, the
OFF-time is stored in the Pulse Timer and is counted down
again. When it reaches zero now, signal OUT is activated
again, ON-time is loaded and the counter starts counting
down etc. On the Pulse Counter reaching zero, an interrupt
(Special Interrupt, SI) is sent to the CPU, indicating that the
Hardware Modulator is ready.
The delay between two pulse bursts is determined by
software. When a new burst must be generated with the
same ON-time and OFF-time values, only the Pulse
Counter is loaded with the required number of pulses and
the Hardware Modulator will start automatically. The
interrupt signal is reset when the Pulse Counter is loaded
or can be reset directly by writing a logic 1 to bit Rint of the
Control Register.
9
There are three different interrupt sources with different
vectors within the PCA84C122, these are:
9.1
The internal timer/counter is the same as in the other
members of the PCF84CXXX family. Instructions
‘EN TCNTI’ and ‘DIS TCNTI’ are to enable/disable
the interrupt.
9.2
9.2.1
The keypad wake-up function generates an interrupt
signal to the CPU. This signal is used to terminate the Stop
mode and thus allows program execution to continue.
If the external interrupt is enabled the microcontroller
executes the instruction immediately following the STOP
instruction, before executing the interrupt routine.
1995 May 01
External keypad wake-up and T0/INT pin;
vector address: 03H
Hardware modulator (SI); vector address: 05H
Internal Timer/counter (TI); vector address: 07H.
8-bit microcontrollers for
remote control transmitters
INTERRUPTS
Operation of the Hardware Modulator
Internal timer/counter
External keypad wake-up and T0/INT pin
K
EYPAD WAKE
-
UP
osc
.
11
If the external interrupt is disabled, program execution
continues with the instruction following the STOP
instruction.
The wake-up function is activated when any of the
sense lines (Port 1 pins) are pulled LOW.
9.2.2
T0/INT must be connected to V
because no internal pull-up or pull-down is present
(floating input).
Because this pin is ‘ANDed’ with Port 1 inputs, the result of
‘JTO’ and ‘JNTO’ instructions and the interrupt depends on
the AND of all Port 1 and T0/INT inputs.
T0/INT can serve as an extra sense line, when a pull-up
resistor is connected, however, multiple keys will not be
detected.
10 OUTPUT DRIVER
The output of the Hardware Modulator is amplified and
able to sink a current of 27 mA when the OUT signal is
active. Therefore, only one external (PNP) transistor is
required to drive the IR-LED.
LOW level output sink current, minimum 27 mA at
V
11 WATCHDOG TIMER (WDT)
The Watchdog timer consists of a 17 stage counter with a
clock of
Register) clears the WDT to zero.
After a Power-on-reset, the WDT is cleared to zero; the
content of the WDT is then incremented by ‘1’ every
30 clock cycles.
If the WDT is not reset to zero before it overflows, a
RESET signal is generated and the device is reset, thus
preventing a lock up or malfunction. The software must
clear the WDT at least 1/f
generates the RESET signal; i.e. at f
1.92 s.
In the Idle mode the oscillator is still running and therefore
the WDT remains active. In the Stop mode, the WDT is
fully stopped and the value of the counter is kept.
DD
= 2.0 V, V
PCA84C122; 222; 422; 622; 822
1
T0/INT
30
f
OUT
osc
PIN
. A logic 1 written to RWDT bit (Control
V
DD
osc
1.0 V.
30
DD
when not in use,
2
osc
Product specification
16
seconds before it
= 1 MHz, this is