4
TIMERS
The IRV-686 SBC has the equivalence of an 82C54 Programmable Timer included in the System
Controller chip. The 82C54 is a three channel Programmable Counter/Timer chip. The three timers
are driven by a 1.19MHz clock source derived from the on-board 14.31818MHz crystal oscillator.
The three timers are used as follows:
TIMER Channel 0: System Timer
TIMER Channel 1: Timer for DRAM refresh
TIMER Channel 2: Tone Generation for Audio
CLOCK/CALENDAR AND CMOS RAM
The IRV-686 SBC includes an MC146818 compatible real time clock/calendar with 128 bytes of
CMOS RAM. An on-board industrial Lithium battery (-40
° to 85°, @ 850mAH) which provides over
10 years of data retention when the system power is off.
The 128 byte CMOS RAM consists of 14 bytes used by the clock/calendar, and 114 bytes used by the
system BIOS.
Should your CMOS become corrupted, i.e. loss of battery power or accidentally clobbered, strange
errors may occur while attempting to run your programs. Jumper JP1 is provided to clear the CMOS
memory, refer to Section 3.0 for instructions on resetting the initial SETUP values. Refer to Appendix
E for the jumper location.
KEYBOARD PORT
The IRV-686 SBC contains an IBM PC/AT compatible keyboard controller for interfacing to a generic
IBM PC/AT compatible keyboard. The keyboard controller assembles the serial data from the
keyboard into bytes and interrupts the CPU via IRQ1 after each byte is ready to be read. The IRQ1
service routine reads port 60H to get the keyboard scan code and acknowledges by sending a
positive pulse to port 61H to clear the interrupt for the next byte. Refer to Appendix D for the
keyboard connector location and pin assignments.
MOUSE PORT
The IRV-686 SBC contains an IBM PS2 compatible mouse port for interfacing to a generic serial
mouse. The mouse port controller assembles the serial data from the mouse into bytes and interrupts
the CPU via IRQ1 after each byte is ready to be read. The IRQ1 service routine reads port 60H to get
the scan code and acknowledges by sending a positive pulse to port 61H to clear the interrupt for the
next byte. Refer to Appendix D for the mouse port connector location and pin assignments.
SPEAKER PORT
The IRV-686 SBC contains an on-board sub-miniature audio speaker to provide audio interface to the
user. Because of the small size of the speaker, the sound output is much reduced over that of the
larger speaker found in most desktop computers. A connector is provided to connect an external
speaker if the sound output is not sufficient. Refer to Appendix D for the speaker port connector
location and pin assignments.
RESET SWITCH
The IRV-686 SBC includes an on-board power detector and power on reset circuit to reset the
computer after power is applied, and to hold the computer reset during low power, brown-out
