am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 25

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

Basic Non-Burst Write
The PCnet-PCI controller uses non-burst write cycles to
access the receive and transmit descriptor entries.
Some of the write accesses to the receive buffer mem-
ory are also in non-burst mode. All PCnet-PCI controller
non-burst write accesses are of the PCI command type
Memory Write (type 7).
Figure 5 shows two non-burst write access within one
arbitration cycle. The PCnet-PCI controller will drop
1-892
DEVSEL
FRAME
AMD
TRDY
IRDY
C/BE
REQ
GNT
CLK
PAR
AD
1
DEVSEL is sampled by the PCnet-PCI controller.
Figure 5. Non-Burst Write Cycles With and Without Wait States
2
3
ADDR
0111
4
P R E L I M I N A R Y
DATA
BE's
PAR
5
Am79C970
PAR
6
FRAME between two consecutive non-burst write cy-
cles. The PCnet-PCI controller will re-request the bus
immediately if it is preempted before starting the second
access. The example below shows an extended cycle
for the first access. The target asserts DEVSEL 2 clock
cycles after the address phase (FRAME asserted) and
adds one extra wait state by asserting TRDY only on
clock 7. The second write cycle in the example shows a
ZERO wait state access.
7
8
ADDR
0111
9
DATA
BE's
PAR
10
PAR
11
18220C-7