5-23 62-11863
5.18 MICROPROCESSOR
The software revision level is noted on a label located on the EPROM chip (component U3 on the
microprocessor logic board). Under NO circumstances should this label be removed.
Under no circumstances should a technician electrically probe the processor at any point,
other than the connector terminals where the harness attaches. Microprocessor components
operate at different voltage levels and at extremely low current levels. Improper use of voltme-
ters, jumper wires, continuity testers, etc. could permanently damage the processor.
Microprocessor Inputs
Some microprocessor inputs operate at voltage levels other than the conventional 12 VDC. Connector points and the
associated approximate voltage levels are listed below for reference only. Under no circumstances should 12 VDC be
applied at these connection points.
Grounded wrist cuffs are available from Carrier (P/N 07-00304-00). It is recommended that these be worn when-
ever handling a microprocessor.
Most electronic components are susceptible to damage caused by electrical static discharge (ESD). In certain
cases, the human body can have enough static electricity to cause resultant damage to the components by touch.
This is especially true of the integrated circuits found on the truck/trailer microprocessor.
ESD Safety
Although there is less danger of electrical static discharge (ESD) damage in the outdoor environment, where the
processor is likely to be handled, proper board handling techniques should always be stressed. Boards should
always be handled by their edges in much the same way one would handle a photograph. This not only precludes
the possibility of ESD damage, but also lowers the possibility of physical damage to the electronic components.
Although the microprocessor boards are fairly rugged when assembled, they are more fragile when separated and
should always be handled carefully.
When welding is required on the unit frame or on the front area of the trailer, ALL wiring to the microprocessor
MUST be disconnected. When welding is performed on other areas of the trailer, the welder ground connection
MUST be in close proximity to the area being welded. It is also a good practice to remove both battery cables
before welding on either the unit frame or the truck to prevent possible damage to other components such as the
alternator and voltage regulator.
a Replacing the Keyboard
Should damage to the keyboard of the microprocessor occur, it is possible to replace only the keyboard.
b Hour Meters
The hour meter can be set to any value via the serial port if the meter has less then five hours on it. This allows a
replacement microprocessor to be set to the same hours as the microprocessor it is replacing.
The microprocessor has two programmable maintenance hour meters, which are set via the serial port. These
maintenance hour meters are compared to one of the hour meters (diesel, standby, or switch on). If the hour meter
is greater than the maintenance hour meter, the proper service alarm is triggered.
Table 5–6 Connection Point Voltage Inputs
Connection Point Approximate Voltage
ATS, CDT, RAS, SAS, WTS 2.5 vdc (Variable)
MP23 5.0 vdc
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