Information Technology Reference
In-Depth Information
3.3.2 82344 IC
Much of the electronics in a PC has been integrated onto single ICs. The 82344 IC is one that
interfaces directly to the ISA bus. Figure 3.7 shows its pin connections.
Figure 3.7
82344 IC connections
3.4
Other legacy busses
Two other busses which were used in the past are:
•
MCA
. IBM developed the Microchannel Interface Architecture (MCA) bus for their
PS/2 computers. This bus is completely incompatible with ISA bus. It can operate as a
16-bit or 32-bit data bus. The main technical difference between the MCA and PC/ISA
(and EISA) is that the MCA is an asynchronous bus whereas PC/ISA/EISA use a syn-
chronous bus. An synchronous bus works at a fixed clock rate whereas an asynchronous
bus data transfer is not dependent on a fixed clock. Asynchronous buses take their tim-
ings from the devices involved in the data transfer (that is, the processor or system
clock). The original MCA specification resulted in a maximum transfer rate of 160
MB/sec. Very few manufacturers have adopted MCA technology and it is mainly found
in IBM PS/2 computers.
•
EISA
. Several manufacturers developed the EISA (Extended Industry Standard Archi-
tecture) bus in direct competition to the MCA bus. It provides compatibility with PC/ISA
but not MCA. The EISA connector looks like an ISA connector. It is possible to plug an
ISA card into an EISA connector, but a special key allows the EISA card to be inserted
