AM79C970A Advanced Micro Devices, AM79C970A Datasheet - Page 56

• Manufacturer Part Number: AM79C970A
• Description: PCnet-PCI II Single-Chip Full-Duplex Ethernet Controller for PCI Local Bus Product
• Manufacturer: Advanced Micro Devices

Initialization Block DMA Transfers
During execution of the PCnet-PCI II controller bus
master initialization procedure, the PCnet-PCI II con-
troller microcode will repeatedly request DMA transfers
from the BIU. During each of these initialization block
DMA transfers, the BIU will perform two data transfer cy-
cles reading one DWord per transfer and then it will re-
linquish the bus. When SSIZE32 (BCR20, bit 8) is set to
ONE (i.e. the initialization block is organized as 32-bit
software structures), there are 7 DWords to transfer dur-
ing the bus master initialization procedure, so four bus
mastership periods are needed in order to complete the
initialization sequence. Note that the last DWord trans-
fer of the last bus mastership period of the initialization
sequence accesses an unneeded location. Data from
this transfer is discarded internally. When SSIZE32 is
cleared to ZERO (i.e. the initialization block is
56
AMD
DEVSEL
FRAME
TRDY
IRDY
C/BE
REQ
GNT
PAR
CLK
AD
1
DEVSEL is sampled
Figure 24. Initialization Block Read In Non-Burst Mode
2
IADD i
0110
3
PAR
P R E L I M I N A R Y
4
0000
Am79C970A
DATA
5
organized as 16-bit software structures), then three bus
mastership periods are needed to complete the
initialization sequence.
The PCnet-PCI II controller supports two transfer
modes for reading the initialization block: non-burst and
burst mode; with burst mode being the preferred mode
when the PCnet-PCI II controller is used in a PCI
bus application.
When BREADE is cleared to ZERO (BCR18, bit 6), all
initialization block read transfers will be executed in
non-burst mode. There is a new address phase for
every data phase. FRAME will be dropped between
the two transfers. The two phases within a bus
mastership period will have addresses of ascending
contiguous order.
PAR
6
IADD i +4
0110
7
PAR
8
0000
DATA
9
PAR
10
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