Little Board/P5x Technical Manual
2–15
Battery-Backed Clock
An AT-compatible battery-backed real-time clock (with CMOS RAM) is standard on the Little
Board/P5x. A 3.0 volt Lithium battery soldered to the board powers the cloc k. Battery d rain fo r the
clock is less than 0.4 uA. This battery will support the clock for more than 10 years of normal
usage.
The factory initializes the real-time clock and various parameters in the configuration memory for a
standard configuration. The factory sets the date and time , but it may n ot be se t for you r time
zone. Use Setup to change these values as needed.
The contents of the configuration memory are also stored in an on-board EEPROM. The ROM BIOS
reads the EEPROM to get configuration information if the CMOS RAM data is lost. This means
that the board will function if the battery fails. Note that without a battery, the re al-time cloc k
date and time will not be correct.
Serial Ports
The Little Board/P5x provides four standard RS-232C serial ports, Serial 1 and Serial 2 at J11, and
Serial 3 and Serial 4 at J13.
All ports support software selectable standard baud rates up to 115.2K bits/second, 5-8 d ata bits,
and 1, 1.5, or 2 stop bits. Note that the IEEE RS-232C specification limits the serial port to 19.2K
bits/second on cables up to 50 feet in length.

I/O Addresses and Interrupt Assignments

The serial ports appear at the standard port addresses as shown in Table 2– 10. Each serial po rt
can be independently disabled using the Setup function, freeing its I/O addresses for use by other
devices installed on the PC/104 and PCI expansion buses.
Table 2– 10 also shows the IRQs assigned to each serial port. Note that these interrupts are shared
resources via serial interrupt protocol. (They do not have PC/104-type interru pt sharing circu its, as
defined in the PC/104 specification.)
Table 2– 10. Serial Port I/O Addresses and Interrupts

Port I/O Address Interrupt

Serial 1 3F8h - 3FFh 4
Serial 2 2F8h - 2FFh 3
Serial 3 3E8h - 3EFh 3, 4, 5, 7, 9,
10, 11, 12
Serial 4 2E8h - 2EFh 3, 4, 5, 7, 9,
10, 11, 12
When a serial port is disabled, its I/O addresses and IRQ are available to other periphe rals
installed on the PC/104 expansion bus. You can disable any of the serial ports u sing Setu p.