Thermal Jet
Appendix B: Theory of Operation
5780-320 Operations Manual Rev C
Page 28
CPU Board
The CPU Board has a microcontroller, flash, SDRAM and SRAM memory, a touch screen
controller, a real time clock/calendar, an Ethernet port, two USB 2.0 ports, two serial ports,
12V, 5V, 3.3V and 1.8V regulators, a 3V battery, PC/104 connectors and connectors for
attaching the system display and keyboard assemblies.
The microcontroller (U20) is the IJ3000-ES's central processing unit (CPU). It executes the
system program from flash (U16, U18) and SDRAM (U15, U17). The CPU also directly
controls the keyboard, detecting and processing key closures. The CPU’s on-board LCD
controller reads display data from the display memory (part of the SDRAM), formats it and
sends it to the LCD with all necessary control signals. Display data is written into the dis-
play memory by the CPU.
The touch screen controller (U27) senses when the screen is touched, and sends screen
coordinate data to the CPU for processing.
The real time clock/calendar (U21) keeps system time.
The 3V battery (BT1) preserves system data and keeps the clock running during power
outages or when the IJ3000-ES is not plugged into a power outlet.
Test Points:
TP1:
12VDC, power for display backlight. Turns on/off with soft power
switch.
TP2:
5VDC, power for 5V logic. Also supplies the input voltage to the
3.3V regulator.
TP3:
3.3VDC, power for 3.3V logic. Also supplies the input voltage to
the 1.8V regulator.
TP4:
1.8VDC, power for the CPU core.
LEDs:
D1:
Ethernet connector, Green. Flashes to indicate network traffic.
D2:
Ethernet connector, Green. Indicates valid network connection.
D3:
Yellow, flashes when the CPU is running.
D7:
Green, indicates 3.3V is present.
