Controllers; Interrupt Controllers; Timers And Counters; Programmable Timers - DIGITAL-LOGIC MICROSPACE PCC-P5 Technical User's Manual

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4.4 Controllers

4.4.1 Interrupt Controllers

An 8259A compatible interrupt controller, within the chipset device, 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
IRQ0 ROM-BIOS clock tick function, from timer 0
IRQ1 Keyboard controller output buffer full
IRQ2 Used for cascade 2. 8259
IRQ3 COM2
IRQ4 COM1
IRQ5 Free for user
IRQ6 Floppy controller
IRQ7 LPT1 parallel printer
IRQ8 Battery backed clock, alarm function of the RTC
IRQ9 Free for user
IRQ10 Ethernet (LAN), standard selection
IRQ11 Free for user
IRQ12 PS/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
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PCCP5 Manual V2.3
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