Information Technology Reference
In-Depth Information
Table 2.4
Near-end cross-talk (dB/100 m) for Cat-3, Cat-4 and Cat-5 cable
Frequency (MHz)
Near end cross-talk (dB/100 m)
Cat-3
Cat-4
Cat-5
1
13.45
18.36
21.65
4
10.49
15.41
18.04
10
8.52
13.45
15.41
16
7.54
12.46
14.17
2.2
Interrupts
An interrupt allows a program or an external device to interrupt the execution of a program.
The generation of an interrupt can occur by hardware (hardware interrupt) or software (soft-
ware interrupt). When an interrupt occurs an interrupt service routine (ISR) is called. For a
hardware interrupt the ISR then communicates with the device and processes any data. When
it has finished the program execution returns to the original program. A software interrupt
causes the program to interrupt its execution and goes to an interrupt service routine. Typical
software interrupts include reading a key from the keyboard, outputting text to the screen and
reading the current date and time. The operating system must respond to interrupts from
external devices, as illustrated in Figure 2.7.
Operating
system
Operating
system
Program requests
Program requests
Program requests
Program requests
Interrupt
controller
Interrupt
controller
Software interrupts
Software interrupts
Interrupt
controller
Interrupt
controller
Interrupt
Service
Routine
(ISR)
Interrupt
Service
Routine
(ISR)
Interrupt
Service
Routine
(ISR)
Interrupt
Service
Routine
(ISR)
Hardware interrupts
Hardware interrupts
Figure 2.7
Interrupt service routine
