83C576 Philips Semiconductors, 83C576 Datasheet - Page 25

• Manufacturer Part Number: 83C576
• Description: 80C51 8-bit microcontroller family 8K/256 OTP/ROM/ 6 channel 10-bit A/D/ 4 comparators/ failure detect circuitry/ watchdog timer
• Manufacturer: Philips Semiconductors

Philips Semiconductors
PWMs
The pulse width modulator system of the 8XC576 contains two
PWM output channels. These channels generate pulses of
programmable length and interval. The prescaler and counter are
common to both PWM channels.
The prescaler is loaded with the complement of the PWMP register
during counter overflow, internal reset, and when EN/CLR# = 0. The
repetition frequency is defined by the 8-bit prescaler which clocks
the counter. The prescaler division factor = PWMP+1. Reading the
PWMP gives the current reload value. The actual count of the
prescaler cannot be read.
The 8-bit counter counts from 0–254 inclusive. The value of the
counter is compared to the contents of the compare registers PWM0
and PWM1. When the counter compares to the compare register,
that register’s output goes LOW. When the counter reaches zero the
output is set HIGH unless PWMn = 00H. The duty cycle of each
channel is defined by the contents of its compare register and is in
the range of 0 to 1, programmed in increments of 1/255.
The outputs can be set continuously low by loading PWMn with 00H
and continuously high by loading with FFH.
The PWM counter is enabled with bit EN/CLR# of the PWCON
register. Output to the port pin is separately enabled by setting the
PWEn bits in the PWCON register. The counter remains active if
EN/CLR# is set even if both PWEn bits are reset. The PWM function
is reset by a chip reset. In idle mode, the PWM will function as
configured by PWCON. In power-down the state of the PWM will
freeze when the internal clock stops. If the chip is awakened with an
external interrupt, the PWM will continue to function from its state
when power-down was entered. The EN/CLR# bit of PWCON will
clear the counter and load the contents of the PWMP into the
prescaler when set LOW. If PWEn is set at this time the output will
go HIGH unless PWMn is 00H.
The repetition frequency is given by:
An oscillator frequency of 12MHz results in a repetition range of
92Hz to 23.5KHz.
The high/low ratio of PWMn is PWMn/(255–PWMn) for PWMn
values except 255. A PWMn value of 255 results in a high PWMn
output.
In order for the PWMn output to be used as a standard I/O pin,
PWMn must be reset. The PWM counter can still be used as an
internal timer by setting EN/CLR#.
1998 Jun 04
80C51 8-bit microcontroller family
8K/256 OTP/ROM, 6 channel 10-bit A/D, 4 comparators,
failure detect circuitry, watchdog timer
f
PWM
(510
(1
f
OSC
PWMP))
25
Pulse Width Modulator Control Register Bit Definitions
(PWCON = BCH)
PWMF
EN/CLR
PWE1
PWE0
Auxiliary Register Bit Definitions (AUXR =8EH)
RST AUXR.3
TXI
LO
AO
Interrupt Enable 0 (IE0) Register
EA
EC
ET2
ES
ET1
EX1
ET0
EX0
Interrupt Enable 1 (IE1) Register
EOB
EIB
EAD
EC4
EC3
EC2
EC1
EC0
Interrupt Priority 0 (IP0) Register
PPC
PT2
PS
PT1
PX1
PT0
PX0
Interrupt Priority 1 (IP1) Register
POB
PIB
PAD
PC4
PC3
PC2
PC1
PC0
AUXR.2
AUXR.1
AUXR.0
IE0.7
IE0.6
IE0.5
IE0.4
IE0.3
IE0.2
IE0.1
IE0.0
IE1.7
IE1.6
IE1.5
IE1.4
IE1.3
IE1.2
IE1.1
IE1.0
IP0.7
IP0.6
IP0.5
IP0.4
IP0.3
IP0.2
IP0.1
IP0.0
IP1.7
IP1.6
IP1.5
IP1.4
IP1.3
IP1.2
IP1.1
IP1.0
PWCON.3
PWCON.2
PWCON.1
PWCON.0
Software reset bit
SIO TxD invert
Low Speed, reduces internal clock drive
ALE Off, when set turns off ALE
Enable all interrupts
Enable PCA interrupt
Enable Timer 2 interrupt
Enable Serial I/O interrupt
Enable Timer 1 interrupt
Enable External interrupt 1
Enable Timer 0 interrupt
Enable External interrupt 0
Enable OBE interrupt
Enable IBF interrupt
Enable ADC interrupt
Enable PCA module 4 interrupt
Enable PCA module 3 interrupt
Enable PCA module 2 interrupt
Enable PCA module 1 interrupt
Enable PCA module 0 interrupt
(reserved)
PCA interrupt priority
Timer 2 interrupt priority
Serial I/O interrupt priority
Timer 1 interrupt priority
External interrupt 1 priority
Timer 0 interrupt priority
External interrupt 0 priority
OBE interrupt priority
IBF interrupt priority
ADC interrupt priority
PCA module 4 interrupt priority
PCA module 3 interrupt priority
PCA module 2 interrupt priority
PCA module 1 interrupt priority
PCA module 0 interrupt priority
Counter overflow flag,
must be cleared by software
Counter enable and counter/prescaler
reset when Low
PWM1 output to P2.7 pin enable
PWM0 output to P2.6 pin enable
83C576/87C576
Product specification