210
Am79C973/Am79C975
P R E L I M I N A R Y
and, therefore, may be set in any
descriptor of a chained buffer
transmission.
29
ADD_FCS
ADD_FCS dynamically controls
the generation of FCS on a frame
by frame basis. This bit should be
set with the ENP bit. However, for
backward compatibility, it is rec-
ommended that this bit be set for
every descriptor of the intended
frame. When ADD_FCS is set,
the state of DXMTFCS is ignored
and transmitter FCS generation is
activated. When ADD_FCS is
cleared to 0, FCS generation is
controlled by DXMTFCS. When
APAD_XMT (CSR4, bit 11) is set
to 1, the setting of ADD_FCS has
no effect on frames shorter than
64 bytes. ADD_FCS is set by the
host, and is not changed by the
Am79C973/Am79C975 control-
ler. This is a reserved bit in the C-
LANCE (Am79C90) controller.
28
MORE/LTINT Bit 28 always functions as
MORE. The value of MORE is
written
Am79C975 controller and is read
by the host. When LTINTEN is
cleared to 0 (CSR5, bit 14), the
Am79C973/Am79C975 controller
will never look at the contents of
bit 28, write operations by the
host have no effect. When LTINT-
EN is set to 1 bit 28 changes its
function to LTINT on host write
operations and on Am79C973/
Am79C975 controller read opera-
tions.
by
the
Am79C973/
MORE
MORE indicates that more than
one retry was needed to transmit
a frame. The value of MORE is
written
by
the
Am79C975 controller. This bit
has meaning only if the ENP bit is
set.
Am79C973/
LTINT
LTINT is used to suppress inter-
rupts after successful transmis-
sion on selected frames. When
LTINT is cleared to 0 and ENP is
set
to
1,
the
Am79C975 controller will not set
TINT (CSR0, bit 9) after a suc-
cessful transmission. TINT will
Am79C973/
only be set when the last descrip-
tor of a frame has both LTINT and
ENP set to 1. When LTINT is
cleared to 0, it will only cause the
suppression of interrupts for suc-
cessful transmission. TINT will al-
ways be set if the transmission
has an error. The LTINTEN over-
rides the function of TOKINTD
(CSR5, bit 15).
27
ONE
ONE indicates that exactly one
retry was needed to transmit a
frame. ONE flag is not valid when
LCOL is set. The value of the
ONE bit is written by the
Am79C973/Am79C975 control-
ler. This bit has meaning only if
the ENP bit is set.
26
DEF
Deferred
Am79C973/Am79C975 controller
had to defer while trying to trans-
mit a frame. This condition occurs
if the channel is busy when the
Am79C973/Am79C975 controller
is ready to transmit. DEF is set by
the Am79C973/Am79C975 con-
troller and cleared by the host.
indicates
that
the
25
STP
Start of Packet indicates that this
is the first buffer to be used by the
Am79C973/Am79C975 controller
for this frame. It is used for data
chaining buffers. The STP bit
must be set in the first buffer of
the frame, or the Am79C973/
Am79C975 controller will skip
over the descriptor and poll the
next descriptor(s) until the OWN
and STP bits are set. STP is set
by the host and is not changed by
the Am79C973/Am79C975 con-
troller.
24
ENP
End of Packet indicates that this
is the last buffer to be used by the
Am79C973/Am79C975 controller
for this frame. It is used for data
chaining buffers. If both STP and
ENP are set, the frame fits into
one buffer and there is no data
chaining. ENP is set by the host
and is not changed by the
Am79C973/Am79C975 control-
ler.
23
BPE
Bus Parity Error is set by the
Am79C973/Am79C975 controller