MU9C8328 Ethernet Interface

Rev. 4a

5

The MU9C8328 works with the MUSIC LANCAMs to

provide a complementary and versatile 10 MHz Ethernet

filtering solution for bridges, routers, and switches. Using

the serial NRZ data stream and clock available from many

Ethernet controller chips, the MU9C8328 parses the

incoming frame, finds the Start Delimiter, and forms the

Destination and Source addresses into 16-bit words for

relay to the LANCAM. After all three 16-bit DA segments

have been loaded into the LANCAM, an automatic

compare occurs between the incoming DA and the 48-bit

MAC addresses stored in the LANCAM. If a match is

found, the MU9C8328 is notified, and if Control Register

bit 5 is set for negative filtering, the /REJECT line will be

asserted if Control Register bit 3 is set. An interrupt can

also be generated over the /INT pin if Control Register bit

8 is set. Also, if Control Register bit 0 is set, the Associated

data in segment 0 of the matching entry in the LANCAM

will be retrieved and stored in the Associated Data register

for reading by the host processor. If a match is not found

on the DA, and Control Register bit 5 was set for positive

filtering, the /REJECT line will be asserted. An interrupt

can also be enabled for a no-match on a DA using Control

Register bit 10.

After the DA filtering, the Source Address is loaded

into the LANCAM in three segments. Upon the last

SA load, an automatic compare again takes place. If

there is a match between the SA and an entry in the

CAM, and Control Register bit 7 was set, an interrupt

is asserted. Positive and negative filtering on the SA is

also possible, set by Control Register bit 4, and the /INT

pin may be asserted as well. In the case of a no-match

on an SA, the SA can be automatically “learned” (i.e.,

moved to the first empty location in the LANCAM) if

Control Register bit 1 is set.

If a Loss of Carrier is detected by SERCLK staying LOW

for more than 16 SYSCLK cycles, an interrupt is triggered

if Control Register bit 12 is set. This interrupt also activates

if a collision is detected.

The host processor can access the MU9C8328, shown in

Table 1, at any time, even when a frame is being processed.

Access to the LANCAM through the LANCAM access

registers (04H to 07H) is arbitrated, however, with the

network having precedence. The host processor can have

control of the LANCAM by setting the Network Enable

bit in the Control register (bit 13) to a 0, which will disable

network filtering until it is returned to a 1. While disabled,

bit 14 in the Control register sets the MU9C8328 to accept

all frames by keeping /REJECT HIGH, or to reject all

frames by keeping /REJECT LOW.

Registers 04H through 07H allow the host processor access

to the LANCAM for Command and Data Write and Read

cycles, with /EC HIGH or LOW. This is often needed for

housekeeping activities, such as preventing the LANCAM

from becoming full by aging out old entries based on

timestamps stored in the Associated data (Segment 0) of

the LANCAM memory.

The /INT pin will go LOW at the end of the SA field to

indicate an interrupt for any of the reasons set in the

Control register. Reading the Status register to discover

the nature of the interrupt will take the /INT pin HIGH

again. The READY signal goes LOW after a host processor

write to a register or the LANCAM to indicate that the

Write cycle has begun and return HIGH after a fixed

number of SYSCLK cycles. It will also go LOW during a

read from the LANCAM and return HIGH when the data

from the LANCAM is valid. Since a network compare

activity has precedence over a host process access to the

LANCAM, READY will stay LOW until the network

activity is complete and the host-induced LANCAM read

has completed.

Figure 1 shows a typical network filtering sequence, where

the MU9C8328’s Control register was set to 2109H. This

setting enables network filtering, enables an interrupt for

a match found on the DA, enables negative filtering on

the DA (reject if a DA match is found), enables asserting

the /REJECT pin for compares on the DA, and enables

retrieving the Associated Data field from the matching

location in the LANCAM.

FUNCTIONAL DESCRIPTION