AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 167

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

Offset 17Ah
Offset 178h
8/01/00
SRAM Boundary Register
15-0
15-0
Bit
Bit
SRAM_SIZE
SRAM_BND
Name
Name
SRAM Boundary. Specifies the size of the transmit buffer portion of the SRAM in units of 512-byte
pages. For example, if SRAM_BND is set to 10, then 5120 bytes of the SRAM will be allocated for
the transmit buffer and the rest will be allocated for the receive buffer.
The transmit buffer in the SRAM begins at address 0 and ends at the address (SRAM_BND*512)-
1. Therefore, the receive buffer always begins on a 512-byte boundary.
SRAM_BND must be initialized to an appropriate value, either by the EEPROM or by the host CPU.
SRAM_BND must be set to a value less than or equal to IFFCh. Values larger than IFFCh will
cause incorrect behavior.
Note: The minimum allowed number of pages for normal network operation is four, and the
maximum is SRAM_SIZE - 4.
This register is an alias of BCR26.
SRAM Size. Specifies the total size of the SSRAM buffer in units of 512-byte pages. For example,
assume that the external memory consists of one 64K X 32 bit SSRAM, for a total of 256K bytes.
In this case SRAM_SIZE should be set to 512 (256K divided by 512).
This field must be initialized to the appropriate value, either by the EEPROM or by the host CPU.
SRAM_SIZE must be set to a value less than or equal to 2000h. Values larger than 2000h will
cause incorrect behavior.
Note: The minimum allowed number of pages is eight for normal network operation.
This register is an alias of BCR25.
Table 76.
Table 77.
P R E L I M I N A R Y
SRAM Boundary Register
Am79C976
SRAM Size Register
All bits in this register are cleared to 0 when the RST
pin is asserted, before the serial EEPROM is read, and
after a serial EEPROM read error.
All bits in this register are cleared to 0 when the RST
pin is asserted, before the serial EEPROM is read, and
after a serial EEPROM read error.
Description
Description
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