Compaq iPAQ Internet Device Manual De Usuario
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.
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.
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]
(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.