83C795 Datasheet, PDF (96/136 Pages) List of Unclassifed Manufacturers – Ethernet System Controller

BUFFER STRUCTURING AND DATA MOVEMENT PROCESSES
83C795
REG
COLCNT
TSTAT
TSTARTH,L
TCNTH, L
TCON
not used
DESCRIPTION
Written with the number of
collisions experiences by the LAN
controller while attempting to
transmit this frame.
This entry in the table is used to
control ownership of the frame
buffer:
TSTAT = 00 means the 83C795
has begun transmission
TSTAT>00 but <FFh means the
frame has been completed and
the contents of the transmit status
register have been moved into
that location.
TSTAT = FFh means assembled
frame has not yet been
transmitted.
Pointer to start of transmit buffer.
16-bits wide.
Number of bytes to transmit,
exclusive of computed FCS.
Transmit configuration desired for
this frame. This entire byte is
DMA’d into the internal TCON
register and applies to this frame.
Ignored by the LAN controller.
8.2 RECEIVE PACKET BUFFERING
T wo alternative modes of buffering received
packets are s upported: ring of buffers and
linked-list. S election between thes e two modes is
made by a bit in the E NH R egister, E NH.ALT E GO.
8.2.1 Ring of Buffers
All received packets are stored in one circularly
connected, contiguous s et of 256-byte buffers . T he
number and location of buffers in the ring is
determined by the values written into the R S TART
and R S T OP R egis ters by the hos t when the
83C795 is initialized. R S T AR T points to the firs t
buffer in the ring and R S T OP points to the buffer
after the las t one in the ring.
E ach packet received will be s tored into one or
moreof thesebuffers , with a4-byteheader ins erted
at the s tart of the firs t buffer.
F igure 8-2 details the format of a received packet
in memory.
TABLE 8-3. MEANING OF DESCRIPTOR
TABLE
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