AM79C973BKD AMD (ADVANCED MICRO DEVICES), AM79C973BKD Datasheet - Page 63

• Manufacturer Part Number: AM79C973BKD
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C973BKD

• Lead Free Status / RoHS Status: Compliant

The exact number of total transfer cycles in the bus
mastership period is dependent on all of the following
variables: the settings of the FIFO watermarks, the
conditions of the FIFOs, the latency of the system bus
to the Am79C973/Am79C975 controller’s bus request,
and the speed of bus operation. The TRDY response
time of the memory device will also affect the number
of transfers, since the speed of the accesses will affect
the state of the FIFO. During accesses, the FIFO may
be filling or emptying on the network end. For example,
on a receive operation, a slower TRDY response will
allow additional data to accumulate inside of the FIFO.
If the accesses are slow enough, a complete DWord
may become available before the end of the bus mas-
tership period and, thereby, increase the number of
transfers in that period. The general rule is that the
longer the Bus Grant latency, the slower the bus trans-
fer operations; the slower the clock speed, the higher
the transmit watermark; or the lower the receive water-
mark, the longer the total burst length will be.
When a FIFO DMA burst operation is preempted, the
Am79C973/Am79C975 controller will not relinquish
bus ownership until the PCI Latency Timer expires.
Figure 30. FIFO Burst Write At End Of Unaligned
DEVSEL
FRAME
TRDY
IRDY
C/BE
REQ
GNT
CLK
PAR
AD
1
DEVSEL is sampled
2
0111
ADD
Buffer
3
DATA
PAR
4
0000
DATA
PAR
5
DATA
1110
PAR
P R E L I M I N A R Y
6
21510D-35
Am79C973/Am79C975
PAR
7
Buffer Management Unit
The Buffer Management Unit (BMU) is a microcoded
state machine which implements the initialization pro-
cedure and manages the descriptors and buffers. The
buffer management unit operates at half the speed of
the CLK input.
Initialization
Am79C973/Am79C975 initialization includes the read-
ing of the initialization block in memory to obtain the op-
erating parameters. The initialization block can be
organized in two ways. When SSIZE32 (BCR20, bit 8)
is at its default value of 0, all initialization block entries
are logically 16-bits wide to be backwards compatible
with the Am79C90 C-LANCE and Am79C96x PCnet-
ISA family. When SSIZE32 (BCR20, bit 8) is set to 1, all
initialization block entries are logically 32-bits wide.
Note that the Am79C973/Am79C975 controller always
performs 32-bit bus transfers to read the initialization
block entries. The initialization block is read when the
INIT bit in CSR0 is set. The INIT bit should be set be-
fore or concurrent with the STRT bit to insure correct
operation. Once the initialization block has been com-
pletely read in and internal registers have been up-
dated, IDON will be set in CSR0, generating an
interrupt (if IENA is set).
The Am79C973/Am79C975 controller obtains the start
address of the initialization block from the contents of
CSR1 (least significant 16 bits of address) and CSR2
(most significant 16 bits of address). The host must
write CSR1 and CSR2 before setting the INIT bit. The
initialization block contains the user defined conditions
for Am79C973/Am79C975 operation, together with the
base addresses and length information of the transmit
and receive descriptor rings.
There is an alter nate method to initial ize the
Am79C973/Am79C975 controller. Instead of initializa-
tion via the initialization block in memory, data can be
written directly into the appropriate registers. Either
method or a combination of the two may be used at the
discretion of the programmer. Please refer to Appendix
A, Alternative Method for Initialization for details on this
alternate method.
Re-Initialization
Th e t ra n s m i tt e r a n d r e c e i ve r s e c ti o n s o f t h e
Am79C973/Am79C975 controller can be turned on via
the initialization block (DTX, DRX, CSR15, bits 1-0).
The states of the transmitter and receiver are moni-
tored by the host through CSR0 (RXON, TXON bits).
The Am79C973/Am79C975 controller should be re-ini-
tialized if the transmitter and/or the receiver were not
turned on during the original initialization, and it was
subsequently required to activate them or if either sec-
tion was shut off due to the detection of an error condi-
tion (MERR, UFLO, TX BUFF error).
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