Controllers; Interrupt Controllers; Timers And Counters; Programmable Timers - DIGITAL-LOGIC MICROSPACE PC/104 Technical User's Manual

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4.4

Controllers

4.4.1

Interrupt Controllers

An 8259A compatible interrupt controller, within the CS4021 device, provides seven prioritized inter-
rupt 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:
IRQ0 ROM-BIOS clock tick function, from timer 0
IRQ1 Keyboard controller output buffer full
IRQ2 Used for cascade 2. 8259
IRQ3 COM2 and COM4 serial port (if present)
IRQ4 COM1 and COM3 serial port (if present)
IRQ5 LPT2 parallel printer (if present)
IRQ6 Floppy controller (if present)
IRQ7 LPT1 parallel printer (if present)
IRQ8 Battery backed clock
IRQ9 Free for user
IRQ10 reserved for Ethernet (LAN)
IRQ11 Free for user
IRQ12 reserved forPS/2 mouse
IRQ13 Math coprocessor
IRQ14 Harddisk IDE / SCSI
IRQ15 Free for user
4.5

Timers and Counters

4.5.1

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 1.190 MHz clock, derived from a 14.318 MHz oscillator, which can be internally divided
down 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 (18.2 Hz)
1 DRAM refresh request timing (15 µS)
2 Speaker tone generation time base
onboard used:
yes
yes
yes
yes
yes
no
yes
yes
yes
no
no
no
(yes)
(yes)
yes
no
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MSM486V Manual V3.22