1996 Jun 27 16
Philips Semiconductors Product specification
8-bit microcontroller with on-chip CAN P8xC592
Notes to the alternative Port functions
1. Port lines P1.6 and P1.7 may be selected as CTX0 and CTX1 outputs of the serial port SIO1 (CAN).
After reset P1.6 and P1.7 may be used as normal I/O ports, if the CAN interface is not used.
2. Unused analog inputs can be used as digital inputs. As Port 5 lines may be used as inputs to the ADC, these digital
inputs have an inherent hysteresis to prevent the input logic from drawing too much current from the power lines
when driven by analog signals.
Channel-to-channel crosstalk should be taken into consideration when both digital and analog signals are
simultaneously input to Port 5 (see Chapter 20).
Fig.8 I/O buffers in the P8xC592 (P1.0 to P1.5, Ports 2, 3, and 4).
handbook, full pagewidth
MGA153
p1
p2
p3
input data
read port pin
2 oscillator
periods
n
strong pull-up
I/O PIN
PORT
1, 2, 3 or 4
+5 V
I1
Q
from port latch
INPUT
BUFFER
9 PULSE WIDTH MODULATED OUTPUTS (PWM)
Two Pulse Width Modulated (PWM) output channels are
available with the P8xC592. These channels provide
output pulses of programmable length and interval.
The repetition frequency is defined by an 8-bit prescaler
PWMP which generates the clock for the counter.
Both the prescaler and counter are common to both PWM
channels. The 8-bit counter counts modulo 255 i.e. from
0 to 254 inclusive. The value of the 8-bit counter is
compared to the contents of two registers:
PWM0 and PWM1.
Provided the contents of either of these registers is greater
than the counter value, the output of PWM0 or PWM1 is
set LOW. If the contents of these register are equal to, or
less than the counter value, the output will be HIGH. The
pulse-width-ratio is therefore defined by the contents of the
register PWM0 and PWM1. The pulse-width-ratio is in the
range of 0 to
255
⁄
255
and may be programmed in
increments of
1
⁄
255
.
The repetition frequency f
PWM
, at the PWMn outputs is
given by:
When using an oscillator frequency of 16 MHz, for
example, the above formula would give a repetition
frequency range of 123 Hz to 31.4 kHz.
By loading the PWM registers with either 00H or FFH, the
PWM outputs can be retained at a constant HIGH or LOW
level respectively. When loading FFH to the PWM
registers, the 8-bit counter will never actually reach this
(FFH) value.
Both output pins
PWMn are driven by push-pull drivers,
and are not shared with any other function.
f
PWM
f
CLK
2 PWMP 1+()× 255×
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