am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 24

• Manufacturer Part Number: am79c970
• Description: Pcnettm-pci Single-chip Ethernet Controller For Pci Local Bus
• Manufacturer: Advanced Micro Devices

DEVSEL
FRAME
Basic Burst Read Cycles
The PCnet-PCI controller provides a burst mode to read
data from the transmit buffer. The burst mode must be
enabled by setting BREADE in BCR18. All PCnet-PCI
controller burst read transfers are of the PCI command
type Memory Read Line (type15). AD[1:0] will both be
ZERO during the address phase indicating a linear burst
order. All four byte enable signals will be ZERO during
TRDY
IRDY
C/BE
REQ
GNT
PAR
CLK
AD
1
DEVSEL is sampled by the PCnet-PCI controller.
2
3
ADDR
1110
4
PAR
Figure 4. Burst Read Cycles
5
0000
P R E L I M I N A R Y
DATA
Am79C970
6
PAR
the data phase as the PCnet-PCI controller always
reads a full 32-bit word when in burst mode.
Figure 4 shows a typical burst read access. The PCnet-
PCI controller arbitrates for the bus, is granted access,
and reads four 32-bit words (DWORD) from system
memory and then releases the bus. All four data phases
in this example take two clock cycles each, which is de-
termined by the timing of TRDY.
7
DATA
8
PAR
9
DATA
10
PAR
11
DATA
12
AMD
18220C-6
PAR
1-891
13