COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 194

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

Some applications using remote normally open switches for sensors call for knowing
whether the sensor is connected. Usually one cannot tell the difference between a
normally open switch and a disconnected one. However, a 10k resistor is connected across
the switch, one can measure the resistance to determine whether the switch is connected.
Usually this requires a linear device such as an additional transistor.
If the switch is connected, a programmable I/O port on a microcontroller that can be
placed in the TRI-STATE mode can detect the presence of the 10k resistor without
additional parts. The following shows an example of this technique using a COP8SAx7.
4-2
COP8SAx7 APPLICATION IDEAS
10K1
CONFIGURE PORT
AS INPUT WITH
WEAK PULLUP
SET PIN HIGH
SWITCH
CHECK
HIGH?
HIGH?
OPEN
SW
PIN
PIN
NO
YES
Figure 4-1 Test Circuit
Figure 4-2 Flow Chart
S1
YES
NO
COP8SAx7 CAN DETECT:
S1
S1 CLOSED
J1
DISCONNECTED
J1
DISCONNECTED
OPEN
RET
J1
G0 Pin on COP8SAx7
T0
CLOSED
SWITCH