1996 Jun 19
27
Philips Semiconductors
Preliminary specification
CAN Serial Linked I/O device (SLIO) with
digital and analog port functions
P82C150
11.3
External oscillator mode
In this mode the P82C150 operates with an external clock
instead with the on-chip RC-oscillator. Figure 14 shows
the application with an external clock.
In this mode the P82C150 can achieve bit rates below
20 kbit/s and above 125 kbit/s. The DPM pulse width is
4
×
t
CLK
of the external clock. The corresponding CAN
identifier bit at Port P0 is set to a logic 0. Therefore only
eight P82C150 based CAN nodes operate within the same
network in external oscillator mode.
11.3.1
N
OTE
The external oscillator mode is not the normal operation
mode.
11.4
Using digital I/O port functions
Figures 12 and 13, show the principle application for
digital input and output.
11.5
Using DPM
The simplest way to generate an analog voltage using the
P82C150 is to apply an external low pass filter at one of
the DPM (Distributed Pulse Modulation) outputs. The
simplest implementation concept is a RC-filter of the first
order (refer to Fig.15). Regarding the selection of the time
constant (edge frequency) of this filter, a trade-off between
minimizing of the ripple voltage for maximum accuracy and
minimum of the settling time has to be considered.
Fig.12 Example for digital input application.
P82C150
+
5 V
P0 to P15
digital
input
MHA072
Fig.13 Example for digital output application.
P82C150
digital
output
P0 to P15
MHA073
Fig.14 P82C150 in external oscillator mode.
handbook, halfpage
P82C150
reset
MHA078
clock
P0/CLK
XMOD
RST
+
5 V
Fig.15 Example for DPM application.
P82C150
analog
output
DPM1(2)
P10(P4)
V
t
V
t
MHA074
If the output is loaded by a resistive load, this will decrease the
accuracy due to the voltage drop across the series resistor. In these
cases a low value for the series resistor should be chosen.
The repetition time of one DPM cycle can be derived from:
OSC
t
CYC
f
=