PCA84C922AP PHILIPS [NXP Semiconductors], PCA84C922AP Datasheet - Page 14

• Manufacturer Part Number: PCA84C922AP
• Description: Microcontrollers for universal infrared remote transmitter applications
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
7
The Hardware Modulator used in the PCA84C92X is the
same as the Hardware modulator used in the PCA84CX22
range of microcontrollers.
The function of the Hardware Modulator is to generate a
coded pulse train which is subsequently converted into an
infrared signal by an IR-LED. It is this coded IR signal that
controls the remote equipment. The number of pulses in
the pulse train, the time between pulse train bursts and the
duty cycle of a pulse are all programmable. A typical pulse
train is shown in Fig.10.
The block diagram of the Hardware Modulator is shown in
Fig.14 and comprises:
These are described in detail in Sections 7.1 to 7.5.
7.1
The duty cycle of the pulse is determined by the contents
of the ON-time and OFF-time Registers. The ON-time
Register controls the active or ON period of the pulse; the
OFF-time Register controls the inactive or OFF period of
the cycle.
The 8-bit ON-time Register resides at address 00H and is
loaded by software. The decimal value of its contents
plus 2, determines the number of oscillator cycles that the
LOUT pin is active. The active period of LOUT can be
calculated as follows:
1997 Oct 22
t
ON
An 8-bit ON-time Register
An 8-bit OFF-time Register
An 8-bit Control Register
A Pulse Timer
A 10-bit Pulse Counter
Control logic.
Microcontrollers for universal infrared
remote transmitter applications
HARDWARE MODULATOR
=
ON-time Register
----------------------------------------------------------------------------------------------------------------------- -
decimal value held in ON-time Register
f
osc
+
2
14
7.2
This 8-bit register resides at address 01H and is loaded by
software. The decimal value of its contents plus 2,
determines the number of oscillator cycles that the LOUT
pin is inactive.
The inactive period of LOUT can be calculated as follows:
7.3
The contents of the ON-time and OFF-time Registers are
loaded alternately into the Pulse Timer. When loaded the
Pulse Timer contents are decremented by ‘1’ every
oscillator cycle and upon reaching zero the Pulse Timer
will be reloaded with the contents of the other register.
7.4
The 10-bit Pulse Counter actually consists of two registers:
the 2-bit Pulse Counter High Register that resides at
address 04H, and the 8-bit Pulse Counter Low Register
that resides at address 02H.
The Pulse Counter is loaded by software; its contents
determine the number of pulses in a specific pulse train.
Loading with zero is not allowed.
7.5
The characteristics of the pulse train are initially
determined by the contents of the ON-time Register, the
OFF-time Register and the Pulse Counter; however, the
HMCTL Register allows these characteristics to be
modified. The Watchdog Timer and derivative interrupt
flag are reset via this register.
t
OFF
=
OFF-time Register
Pulse Timer
Pulse Counter
Hardware Modulator Control Register (HMCTL)
-------------------------------------------------------------------------------------------------------------------------- -
decimal value held in OFF-time Register
PCA84C922; PCA84C923
f
osc
Product specification
+
2