Little Board/P5x Technical Manual
2–9
connector, J10. This will supply +12V to the ISA and PCI portions of the PC/104 expansion bu sses.
Similarly, you can connect -12V and -5V to J16, the Utility Connector, to supply those vo ltages to
both expansion busses. Pinouts for the Utility Connector are provide d in Table 2- 45.
If a PCI expansion card requiring 3.3V is installed, that voltage can be connected to J10-5 to supp ly
power to J21, the PCI bus interface connector.
Switching Power Supplies
If you use a switching power supply, be sure it regu lates pr ope rly w ith the load y our sy stem d raws.
Some switching power supplies do not regulate properly unle ss they are loade d to so me minimum
value. If this is the case with your supply, consult the manufac turer about add itional lo ading , or
use another supply or another type of power source (such as a linear supply, batteries, etc.). The
minimum power for the Little Board/P5x appears in the power specifications in Chapter 1.
Powerfail NMIThe Little Board/P5x includes a circuit that can sense a power failure. If the +5V power supply falls
below ~4.7 V, the powerfail logic produces a non-maskable interrupt (NMI).
When an NMI occurs, the BIOS detects the NMI and displays the message “Power Fail NMI” on the
console. At this point you have two options via the keyboard. You can mask the NMI and continue
(the PC architecture provides a mask bit for the non-maskable interrupt), or reboot the system.
If you want your system to respond to the NMI, you can provide an NMI handler in your
application, and patch the NMI interrupt vector address to point to your routine.
Backup BatteryReal-Time Clock Battery
The real-time clock backup battery on the Little Board/P5x should last 10 years under normal
usage.
Cooling RequirementsThe Pentium CPU, DRAM module, video controller, and core logic chips draw most of the power and
generate most of the heat. The board is designed to support various speed versions of the Pentium
from 133 MHz to 266 MHz with 66 MHz clocks. Since CPU speeds offered by manufacturers are
continuing to increase, contact your Ampro sales representative for the currently available speeds.
A heat sink or fan assembly is provided for the CPU. The fan gets its +5V powe r from J28. J28
power can be controlled by a CPU thermal sensor, as described below.
Table 2– 5 shows the maximum ambient temperature for a CPU case temperature of 70 °C at
various airflow values for various models of the Little Board/P5x. (Values for the 133, 166, and 266
MHz CPUs are given for an 85 °C CPU case temperature.) These numbers are based on typical
power consumption.
Table 2– 5. Airflow vs. Maximum Ambient Temperature