Chapter 3 — Theory of Operation
CV30 Fixed Mount Computer Service Manual 61
Internal Temperature Measurement
The PIC is also connected to an internal thermistor that can be read at the
same time as the battery temperature thermistor to get an internal
temperature for the unit.
Miscellaneous Signal
PIC port pin RE2 can be used in two different ways depending on design
needs. The first is for control of the regulator that generates the core power
for the main processor. The second is the input of SYS_EN signal from the
processor to determine when the main processor is in DEEP SLEEP mode.
The way the signal is used is determined by how the 0 ohm resistors are
loaded on the board to route the desired signal to the PIC.
EEPROM Configuration Information
The PIC has a block of EEPROM that is used to store configuration
information. The configuration information is loaded at the time of
manufacture and must accurately match the hardware options and
configurations of the CV30. The system software determines the
functionality of the CV30 based on the configuration information. This
EEPROM is non-volatile so this vital information is never lost. It is very
important that if a unit is updated in service, or repaired (if the MLB is
replaced, this EEPROM must be updated), the EEPROM must be
correctly loaded or the unit will not function properly.
PIC Controller Programming
The PIC controller is preprogrammed before it is mounted onto the PCB.
In the event that the internal code needs updating, a utility can be run from
the main processor that can download new code to the PIC via the I2C
port. It can then reload its internal flash with the new code.
In the event that this process fails or was aborted in mid update, a dedicated
interface is available to reprogram the PIC. This can be accomplished
without disassembly of the unit. A special programming device is attached
to the MLB via a special adapter card that test engineering uses during
manufacturing test. This adapter connects to the surface contacts on the
MLB inside the SD card slot.
Audio System
The audio system is comprised of the following elements:
• Main processor with AC97 code interface
• AC97 CODEC
• Headphone jack
• Internal speakers and microphones
• Bluetooth digital audio interface
• Audio power supplies
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