~ National ~ Semiconductor - Al Kossow's Bitsavers

Although Cheapernet is intended for local use, several 185
meter segments can be joined together with simple repeaters
to provide for a larger network span. Similarly, several
Cheapernet segments can be tied into a longer Ethernet
"backbone". In this hybrid configuration, the network combines
all the benefits of Cheapernet, flexibility and low cost,
with the ruggedness and the much larger geographic range
of standard Ethernet. Figure 1 illustrates a typical hybrid
LAN configuration.
,r BNC "T" CONNECTOR
(=5=';:~
r "BACKBONE" ETHERNET CABLE
1====[1]
__ THIN CHEAPERNET
CABLE (RG58A/U)
[i] = 50 OHM TERMINATION
FIGURE 1. A Hybrid EthernetlCheapernet System
TRANSMITTING AND RECEIVING PACKETS WITH THE DP8390 CHIPSET
TLlF/8689-3
Node Block Diagram
CO AX
CA BlE
TAP
OR­
BNC
~ -
TRANSCEIVER OR MAU
r--
...
I
S
DP8392 0
L
COAX
A
TRANSCEIVER T
INTERFACE I
0
N
"'-
TRANSCEIVER
CABLE
The node electronics is integrated into three chips, the
DP8390 Network Interface Controller (NIG), the DP8391 Serial
Network Interface (SNI), and the DP8392 Coaxial Transceiver
Interface (CTI). To transmit a packet, the host processor
issues a transmit command to the NIC, which normal-
STATION OR OTE
-
... ...
H
0
DP8391 DP8390 S
SERIAL NETWORK T
NETWORK
INTERFACE
INTERFACE CONTROLLER
B
U
S
TL/F/8689-4
Iy transfers the data to a local buffer memory. The NIC then
automatically handles the transmission of the packet (from
the local buffer through an on-board FIFO to the SNI) according
to the CSMA/CD protocol. The packet has to be in
the following format:
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