am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 29

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

Target Abort
Figure 9 shows a target abort sequence. The target as-
serts DEVSEL for one clock. It then deasserts DEVSEL
and asserts STOP on clock 4. A target can use the target
abort sequence to indicate that it cannot service the data
transfer and that it does not want the transaction to be
retried. Additionally, the PCnet-PCI controller cannot
make any assumption about the success of the previous
data transfers in the current transaction. The PCnet-PCI
controller terminates the current transfer with the
deassertion of FRAME on clock 5 and one clock cycle
later with the deassertion of IRDY. It finally releases the
bus on clock 6.
1-896
AMD
DEVSEL
FRAME
TRDY
STOP
IRDY
C/BE
REQ
GNT
PAR
CLK
AD
1
DEVSEL is sampled by the PCnet-PCI controller.
ADDR
0111
Figure 9. Target Abort
P R E L I M I N A R Y
2
DATA
Am79C970
PAR
3
0000
Since data integrity is not guaranteed, the PCnet-PCI
controller cannot recover from a target abort event. The
PCnet-PCI controller will reset all CSR and BCR loca-
tions to their H_RESET values. Any on-going network
activity will be stopped immediately. The PCI configura-
tion registers will not be cleared. RTABORT (bit 12) in
the Status register will be set to indicate that the PCnet-
PCI controller has received a target abort.
PAR
4
5
6
18220C-11