AMD
66
Am79C940
TDTREQ
will be asserted identi-
cally in both normal and burst
modes, when there is sufficient
space in the XMTFIFO to allow
the specified number of write
cycles to occur (programmed by
the XMTFW bits).
Cleared by activation of the
RESET
pin or SWRST bit.
Receive Burst. When set, the re-
ceive burst mode is selected. The
behavior of the Receive FIFO low
watermark, and hence the de-
assertion of
RDTREQ
, will be
modified.
RDTREQ
will de-assert
when there are only 2-bytes of
data available in the RCVFIFO
(so that a full word read can still
occur).
RDTREQ
will be asserted identi-
cally in both normal and burst
modes, when a minimum of
64-bytes have been received for
a new frame (or a runt packet has
been received and RPA is set).
Once the 64-byte limit has been
exceeded,
RDTREQ
will be as-
serted providing there is suffi-
cient data in the RCVFIFO to
exceed the threshold, as pro-
grammed by the RCVFW bits.
Cleared by activation of the
RESET
pin or SWRST bit.
Bit 0
RCVBRST
MAC Configuration
Control (MACCC)
This register programs the transmit and receive opera-
tion and behavior of the internal MAC engine. All bits
within the MAC Configuration Control register are
cleared upon hardware or software reset. Bit assign-
ments are as follows:
(REG ADDR 13)
PROM DXMT2PD EMBA RES DRCVPA
DRCVBC ENXMT ENRCV
Bit
Name
Description
Bit 7
PROM
Promiscuous. When PROM is
set all incoming frames are re-
ceived regardless of the destina-
tion address. PROM is cleared
by activation of the
RESET
pin or
SWRST bit.
Disable Transmit Two Part De-
ferral. When set, disables the
transmit two part deferral option.
DXMT2PD is cleared by activa-
tion of the
RESET
pin or SWRST
bit.
Bit 6
DXMT2PD
Bit 5
EMBA
Enable Modified Back-off Algo-
rithm. When set, enables the
modified
backoff
EMBA is cleared by activation of
the
RESET
pin or SWRST bit.
Reserved. Read as zeroes. Al-
ways write as zeroes.
Disable Receive Physical Ad-
dress. When set, the physical ad-
dress detection (Station or node
ID) of the MACE device will be
disabled. Packets addressed to
the nodes individual physical ad-
dress will not be recognized (al-
though the packet may be
accepted
by
mechanism).
cleared by activation of the
RESET
pin or SWRST bit.
Disable
Receive
When set, disables the MACE
device from responding to broad-
cast messages. Used for proto-
cols
that
do
broadcast addressing, except as
a function of multicast. DRCVBC
is cleared by activation of the
RE-
SET
pin or SWRST bit (broad-
cast messages will be received).
Enable
Transmit.
ENXMT = 1 enables transmis-
sion. With ENXMT = 0, no trans-
mission will occur. If ENXMT is
written as 0 during frame trans-
mission, a packet transmission
which is incomplete will have a
guaranteed CRC violation ap-
pended before the internal
Transmit FIFO is cleared. No
subsequent attempts to load the
FIFO should be made until
ENXMT is set and
TDTREQ
is
asserted. ENXMT is cleared by
activation of the
RESET
pin or
SWRST bit.
Enable Receive. Setting ENRCV
= 1 enables reception of frames.
With ENRCV = 0, no frames will
be received from the network into
the internal FIFO. When ENRCV
is written as 0, any receive frame
currently in progress will be com-
pleted (and valid data contained
in the RCVFIFO can be read by
the host) and the MACE device
will enter the monitoring state for
missed packets. Note that clear-
ing the ENRCV bit disables the
algorithm.
Bit 4
RES
Bit 3
DRCVPA
the
EADI
DRCVPA
is
Bit 2
DRCVBC
Broadcast.
not
support
Bit 1
ENXMT
Setting
Bit 0
ENRCV