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INTERRUPT CONTROLLER
The IRV-3702 SBC has the equivalence of two 82C59A interrupt controllers included in the System
Controller chip. The controllers accept requests from peripherals, resolve priorities on pending
interrupts and interrupts in service, interrupt the CPU, and provide the vector address of the interrupt
service routine. The two interrupt controllers are cascaded in a fashion compatible with the IBM
PC/AT. The interrupt priority and assignments are shown below in descending order of priority:
Highest IOCHCK/ Parity Check (Non-maskable)
IRQ0 System Timer (Not Available)
IRQ1 Keyboard (Not Available)
IRQ8 Real Time Clock (Not Available)
IRQ9 VGA Controller
IRQ10 Not Used
IRQ11 Not Used
IRQ12 Not Used
IRQ13 Co-processor (Not Available)
IRQ14 EIDE Disk Controller
IRQ15 Not Used
IRQ3 Serial Port 2
IRQ4 Serial Port 1
IRQ5 Alternate for Parallel Port
IRQ6 Floppy Disk Controller
Lowest IRQ7 Parallel Port
The interrupt request lines IRQx and IOCHCK/ are available on the 98-pin edge connector except as
noted above.
TIMERS
The IRV-3702 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-3702 SBC includes a DS12B887 real time clock/calendar with 128 bytes of CMOS RAM and
integral Lithium battery 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.
KEYBOARD PORT
The IRV-3702 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