
AMD
P R E L I M I N A R Y
62
Am79C965
18219B-15
ADS
Ti
BCLK
T1
T2
T1
T2
T1
T2
A4–A31,
M/
IO, D/C
A2–A3,
BE0–BE3
RDYRTN
W/
R
BRDY
BLAST
D0–D31
T1
T2
T1
T2
Ti
From
PCnet-32
From
PCnet-32
From
PCnet-32
From
PCnet-32
From
PCnet-32
Figure 12. FIFO DMA Write
Note that A[1:0] do not exist in a 32-bit system, but both
of these bits do exist in the buffer pointers that are
passed to the PCnet-32 controller in the descriptor.
A[1:0] values will be decoded and presented on the bus
as byte enable (
BE0-BE3) values during FIFO DMA
transfers.
Linear Burst DMA Transfers
Once the PCnet-32 controller has been granted bus
mastership, the PCnet-32 controller may request to per-
form linear burst cycles by de-asserting the
BLAST sig-
nal. If the device being accessed wishes to support
linear bursting, then it must assert
BRDY and de-assert
RDYRTN, with the same timing that RDYRTN would
normally be provided. Linear bursting is only performed
by the PCnet-32 controller if the BREADE and/or
BWRITE bits of BCR18 are set. These bits individually
enable/disable the ability of the PCnet-32 controller to
perform linear burst accesses during master read op-
erations and master write operations, respectively. Only
FIFO data transfers will make use of the linear
burst mode.
The first transfer in the linear burst will consist of both an
address and a data cycle, but subsequent transfers will
contain data only, until the LINBC upper limit of transfers
have been executed. LINBC is a value from the BCR18
register. The linear burst “upper limit” is created by tak-
ing the BCR18 LINBC[2:0] value and multiplying by 4.
The result is the number of transfers that will be per-
formed within a single linear burst sequence.
The entire address bus will still be driven with appropri-
ate values during the data cycles. When the LINBC
upper limit of data transfers have been performed, a
new
ADS may be asserted (if there is more data to be
transferred), with a new address on the A2–A31 pins.
Following the new
ADS cycle, the linear bursting of data
will resume. Ownership of the bus will be maintained
until other variables cause the PCnet-32 controller
to relinquish the bus. These variables have been
discussed in the FIFO DMA transfers section above.
They will be reviewed again within this section of the
document.