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Chapter 4 System Support
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
4-16
4.5 INTERVAL TIMER
The interval timer generates pulses at software (programmable) intervals. A 8254-compatible
timer is integrated into the 82801 component. The timer function provides three counters, the
functions of which are listed in Table 4-7.
Table 4-7.
Interval Timer Functions
Table 4-7.
Interval Timer Functions
Counter Function Gate Clock In Clock Out
0 System Clock Always on 1.193 MHz IRQ0
1 Refresh Always on 1.193 MHz Refresh Req.
2 Speaker Tone Port 61, bit<0> 1.193 MHz Speaker Input
The interval timer is controlled through the I/O mapped registers listed in Table 4-8.
Table 4-8.
Interval Timer Control Registers
Table 4-8.
Interval Timer Control Registers
I/O Port Register
040h Read or write value, counter 0
041h Read or write value, counter 1
042h Read or write value, counter 2
043h Control Word
4.6 SYSTEM CLOCK DISTRIBUTION
These systems use a CK133 clock generator (for 820-based systems) or a CK Whitney or
ICS92250-16 clock generator (for 810/810e-based systems). Table 4-9 lists the system board
clock signals and how they are distributed.
Table 4-9.
Clock Generation and Distribution
Table 4-9.
Clock Generation and Distribution
Frequncy/Signal Source Destination
66, 100, or 133 MHz
(CPUCLK) [1]
CLK Gen. Processor, GMCH
100 MHz CK DIMM sockets
48 MHz “ 82801 ICH, 47B277 I/O Cntlr.
33 MHz (PCICLK) “ 82801 ICH
14.31818 MHz Crystal CK133
14.31818 MHz CLK Gen 82801 ICH
NOTE:
[1] Depending on processor speed.