User manual

DIGITAL-LOGIC AG MSM800SEV/SEL/BEV/XEV/XEL Detailed Manual V1.5

4.5. Controllers

4.5.1. 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 Onboard use

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 yes

IRQ15 Free for user no *

* May depend on the LAN configuration

4.6. Timers and Counters

4.6.1. 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