Information Technology Reference
In-Depth Information
The PCI bus transfers data using the system clock, and can operate over a 32-bit or 64-bit
data path. The high transfer rates used in PCI architecture machines limit the number of PCI
bus interfaces to two or three (normally the graphics adapter and hard disk controller). If data
is transferred at 64 bits (8 bytes) at a rate of 33 MHz then the maximum transfer rate is
264 MB/s. Figure 4.1 shows the PCI architecture. Notice that an I/O bridge gives access to
ISA, IDE and USB. Unfortunately, to accommodate for the high data rates and for a reduc-
tion in the size of the interface card, the PCI connector is not compatible with PC, ISA or
EISA.
The maximum data rate of the PCI bus is 264 MB/s, which can only be achieved using
64-bit software on a Pentium-based system. On a system based on the 80486 processor this
maximum data rate will only be 132 MB/s (that is, using a 32-bit data bus).
The PCI local bus is a radical redesign of the PC bus technology. Table 4.1 lists the pin
connections for the 32-bit PCI local bus and it shows that there are two lines of connections,
the A and the B side. Each side has 64 connections giving 128 connections. A 64-bit, 2ยท94-
pin connector version is also available. The PCI bus runs at the speed of the motherboard
which for the Pentium processor is typically 33 MHz.
Table 4.1
32-bit PCI local bus connections
Pin
Side A
Side B
Pin
Side A
Side B
1
-12V
32
AD17
AD16
TRST
2
TCK
+12V
33
+3.3V
C / BE2
3
GND
TMS
34
GND
FRAME
4
TDO
TDI
35
GND
IRDY
5
+5V
+5V
36
+3.3V
TRDY
6
+5V
37
GND
INTA
DEVSEL
7
38
GND
INTB
INTC
STOP
8
+5V
39
+3.3V
INTD
LOCK
9
Reserved
40
SDONE
PRSNT1
PERR
10
Reserved
+5V(I/O)
41
+3.3V
SBO
11
Reserved
42
GND
PRSNT2
SERR
12
GND
GND
43
+3.3V
PAR
13
GND
GND
44
AD15
C / BE1
14
Reserved
Rese
rved
45
AD14
+3.3V
15
GND
46
GND
AD13
RST
16
CLK
+5V(
I/O)
47
AD12
AD11
17
GND
48
AD10
GND
GNT
18
GND
49
GND
AD09
REQ
19
+5V(I/O)
Reserved
50
KEY
KEY
20
AD31
AD30
51
KEY
KEY
21
AD29
+3.3V
52
AD08
C / BE0
22
GND
AD28
53
AD07
+3.3V
23
AD27
AD26
54
+3.3V
AD06
24
AD25
GND
55
AD05
AD04
25
+3.3V
AD24
56
AD03
GND
26
IDSEL
57
GND
AD02
C / BE3
27
AD23
+3.3V
58
AD01
AD00
28
GND
59
+5V(I/O
)
+5V(I/O
)
FRAME
29
AD21
AD20
60
ACK64
REQ64
30
AD19
GND
61
+5V
+5V
31
+3.3V
62
+5V
+5V
TRDY
