AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 95

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

The Am79C976 controller uses external SSRAM for re-
ceive and transmit FIFOs. The size of the SSRAM can
be up to 4 Mbytes, organized as 1M X 32 bits. The size
of the SSRAM is indicated by the contents of the
SSRAM Size Register (or BCR25). SRAM_SIZE
should be loaded from the EEPROM.
The SSRAM is programmed in units of 512-byte pages.
To specify how much of the SSRAM is allocated to
transmit and how much is allocated to receive, the user
should program SRAM_BND Register (or BCR26, bits
15-0) with the page boundary where the receive buffer
begins. The SRAM_BND is also programmed in units
of 512-byte pages. The transmit buffer space starts at
0000h. It is up to the user or the software driver to split
up the memory for transmit or receive; there is no de-
faulted value. The minimum SSRAM size required is
8/01/00
ERA[19:0]
ROMCLK
ERD[7:0]
ERA[19:0]
ROMCLK
ERD[7:0]
FLWE
FLOE
FLCS
FLWE
FLOE
FLCS
P R E L I M I N A R Y
Am79C976
four 512-byte pages for each transmit and receive
queue, which limits the SSRAM size to be at least 4
Kbytes.
The SRAM_BND upon H_RESET will be reset to
0000h. SRAM_BND must be programmed to a non-
zero value if the transmitter is enabled. SRAM_BND
should be programmed to a value larger than the max-
imum frame size to use the automatic retransmission
options, REX_UFLO, REX_RTRY, and RTRY_LCOL,
or if the transmit FIFO start point, XMTSP, is set to Full
Frame. (XMTSP is CTRL1, bits 17-16, or CSR80, bits
11-10.)
The Am79C976 controller does not allow software di-
agnostic access to the SRAM as do older devices in the
PCnet family. The Am79C976 controller provides soft-
ware access to an internal memory built-in self-test
(MBIST) controller which runs extensive, at-speed
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