am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 36

• Manufacturer Part Number: am79c974
• Description: Pcnettm-scsi Combination Ethernet And Scsi Controller For Pci Systems
• Manufacturer: Advanced Micro Devices

Basic Burst Write Cycles
All Am79C974 controller burst write transfers are of the
PCI command type Memory Write (type 7). AD[1:0] will
both be ZERO during the address phase indicating a lin-
ear burst order. All four byte enable signals will be ZERO
during the data phase as the Am79C974 controller al-
ways writes a full 32-bit word when in burst mode.
Figure 10 shows a typical burst write access. The
36
AMD
DEVSEL
FRAME
TRDY
IRDY
C/BE
REQ
GNT
PAR
CLK
AD
1
DEVSEL is sampled by the Am79C974 controller.
2
3
Figure 10. Burst Write Cycles
ADDR
0111
P R E L I M I N A R Y
4
Am79C974
DATA
PAR
5
0000
Am79C974 controller arbitrates for the bus, is granted
access, and writes four 32-bit words (DWORDs) from
system memory and then releases the bus. In this ex-
ample, the memory system extends the data phase of
the first access by one wait state. The following three
data phases take one clock cycle each, which is deter-
mined by the timing of TRDY.
PAR
6
DATA
7
DATA
PAR
8
DATA
PAR
9
PAR
10
18681A-14