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DIGITAL-LOGIC AG MSEBX800/900 Detailed Manual V1.0
35
5.3. Controllers
5.3.1. Interrupt Controllers
An 8259A compatible interrupt controller, within the chipset, provides seven prioritized interrupt levels. Of
these, several are normally associated with the board's onboard device interfaces and controllers, and
several are available on the AT expansion bus.
Interrupt Sources Used Onboard
IRQ0 ROM-BIOS clock tick function, from timer 0 Yes
IRQ1 Keyboard controller output buffer full Yes
IRQ2 Used for cascade 2. 8259 Yes
IRQ3 COM2 serial port Yes
IRQ4 COM1 serial port Yes
IRQ5 LPT2 parallel printer (if present) No
IRQ6 Floppy controller Yes
IRQ7 LPT1 parallel printer Yes
IRQ8 Battery backed clock Yes
IRQ9 Free for user No
IRQ10 Free for user No
IRQ11 Free for user No
IRQ12 PS/2 mouse Yes
IRQ13 Math. coprocessor Yes
IRQ14 Hard disk IDE / SCSI Yes
IRQ15 Free for user No
It may depend on the LAN configuration.
IRQ 15 = if option CF is not assembled, then free for user.
5.3.2. Timers and Counters
5.3.2.1. Programmable Timers
An 8253 compatible timer/counter device is also included in the board's ASIC device. This device is utilized
in precisely the same manner as in a standard AT implementation. Each channel of the 8253 is driven by a
1.190MHz clock, derived from a 14.318MHz oscillator, which can be internally divided in order to provide a
variety of frequencies.
Timer 2 can also be used as a general purpose timer if the speaker function is not required.
Timer Assignment
Timer Function
0 ROM-BIOS clock tick (18.2Hz)
1 DRAM refresh request timing (15µs)
2 Speaker tone generation time base
5.3.2.2. Watchdog
The watchdog timer detects a system crash and performs a hardware reset. After power up, the watchdog is
always disabled as the BIOS does not send strobes to the watchdog. In case the user wants to take
advantage of the watchdog, the application must produce a strobe at least every 800ms. If no strobe occurs
within the 800ms, the watchdog resets the system.
5.3.3. Core BIOS Download
See the separate driver/software/BIOS manual, GEODE_LX800-900.