am79c961 Advanced Micro Devices, am79c961 Datasheet - Page 31

• Manufacturer Part Number: am79c961
• Description: Pcnettm-isa Jumperless Single-chip Ethernet Controller For Isa
• Manufacturer: Advanced Micro Devices

Shared Memory Mode
System Interface
The Shared Memory mode is the other fundamental op-
erating mode available on the PCnet-ISA
The PCnet-ISA
buffer architecture as the LANCE, but these data struc-
tures are stored in static RAM controlled by the
PCnet-ISA
memory resource to the PC. The other resources look
the same as in the Bus Master mode.
The Boot PROM is selected by an external device which
drives the Boot PROM Address Match (BPAM) input to
the PCnet-ISA
can perform two 8-bit accesses from the 8-bit Boot
PROM and presents 16-bits of data. The shared mem-
ory works the same way, with an external device
generating Shared Memory Address Match and the
PCnet-ISA
the 8 to 16-bit data conversion.
Converting shared memory accesses from 8-bit cycles
to 16-bit cycles allows use of the much faster 16-bit cy-
cle timing while cutting the number of bus cycles in half.
Bus
ISA
Address
+
+
System
24-Bit
controller performing the read or write and
System
controller. The static RAM is visible as a
16-Bit
Data
+
+
controller uses the same descriptor and
controller. The PCnet-ISA
SD[0-15]
SA[0-19]
LA[17-23]
IRQ15/APCS IRQ12/FlashWE
Plug and Play Compatible with Flash Support
PCnet-ISA
Controller
+
Bus Master Block Diagram
+
+
controller.
controller
P R E L I M I N A R Y
PRDB[2]/EEDO
PRDB[0]/EESK
PRDB[1]/EEDI
PRDB[0-7]
Am79C961
SHFBUSY
BPCS
EECS
VCC
This raises performance to more than 400% of what
could be achieved with 8-bit cycles. Converting boot
PROM accesses to 16-bit cycles allows the two memory
resources to be in the same 128 Kbyte block of memory
without a clash between two devices with different data
widths.
The PCnet-ISA
comparator to perform SRAM prefetches on the Private
Data Bus; the SA0-15 signals are used internally to de-
termine whether a SRAM read cycle prefetch is a match
or a miss.
Access to the Ethernet controller registers, board con-
figuration registers, and Address PROM is done with
on-chip address comparators.
Network Interface
The PCnet-ISA
802.3 network via one of two network interface ports.
The Attachment Unit Interface (AUI) provides an IEEE
802.3 compliant differential interface to a remote MAU
or an on-board transceiver. The 10BASE-T interface
provides a twisted-pair Ethernet port. The PCnet-ISA
controller provides three modes of network interface
+
+
controller can be connected to an IEEE
controller uses an internal address
A[0-4]
D[0-7]
A[0-15]
D[0-7]
OE
SK
DI
DO
CS
EEPROM
Address
PROM
Flash
IEEE
ORG
WE
CS
G
AMD
V
18183B-7
CC
1-505
+