Fluke Biomedical 10100AT - Manual (Page 49)

Theory of Operation
Power Supply
3
3-3
directly at the battery terminals (it is separated from the terminals by the fuse and other components not
shown), the measured value will be several tenths of a volt below that measured directly at the terminals.
3.4 Front Panel Switches
The eight front panel switches are of the momentary contact type and are continuously monitored by the
microcomputer for detection of contact closure. At the detection of any contact closure, the
microcomputer scans the switch set to determine which key was pressed and then takes the appropriate
action. The dedicated function of each key is described in section 2 of this manual and will not be
repeated here.
3.5 Microcomputer
The microcomputer is based on the Motorola 68HC11 microcontroller and includes 64 k-bytes of factory-
programmed memory (EPROM). The EPROM contains all of the executable code (firmware) as well as
the descriptions of all built-in customization items (including the standard filter packs, nominal ion
chambers, and standard radiographic units). Also contained within this functional block are 8 k and 64 k
byte blocks of RAM memory.
These are used to hold the data variables required for execution of the internal program, and the storage
of 32,000 kV data points (6.4 s worth at a sampling rate of 5 kHz), respectively.
A 512-byte block of nonvolatile memory (EEPROM) is provided. A portion of the EEPROM is
automatically reprogrammed during each power-down sequence to hold all front panel selections made
by the user. Thus, the ion chamber, filter pack, units, temperature, pressure, and frame/second settings
in effect at power down are automatically restored at the next power up. The EEPROM is also used to
hold all of the internal electrical calibration factors for the unit, as well as all of the customization
selections installed by the user over the RS-232 via the customization program (see the Model 35050A
Programmer's Instruction Manual).
3.6 Display
All display functions are handled by a 2 line by 20-character alphanumeric PLED (polymer LED) module.
The module is under the direct control of the microcomputer and is capable of displaying all ion
chamber/kV filter pack identification strings, numerical measurement results with their appropriate units,
as well as other informational items including the battery voltage, calibration date, etc. Multiple
informational items may be displayed simultaneously (e.g., exposure, time, and kVp measurement
values). The display of kV waveform is left to an external computer.
3.7 Serial Communications Port
A computer interface has been provided in the form of a DCE configured RS-232 port. This port is
configured for operation at 9600 baud and uses a standard Xon/Xoff handshaking protocol (described in
the Model 35050A Programmer's Instruction Manual). The connector type is RJ-45. This interface
facilitates production testing and calibration of the unit, and provides to the user a method of achieving
fully programmable operation as well as waveform display from a PC.
Since there is a power requirement associated with operating the serial communications port, a
mechanism for automatically sensing the presence of an external computer has been provided. The
sensing method involves the detection of a nonzero voltage at the data terminal ready line (DTR) on the
RS-232 connector. The RS-232 interface circuits are powered only when it is sensed that an external
computer is connected.