AM79C976 datasheet(160/309 Pages) AMD

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Am79C976

8/01/00

P R E L I M INARY

MAX_LAT_A: PCI Maximum Latency Alias Register

Offset 1B1h

This register is a writable alias of the Maximum Latency

field at offset 3Fh in PCI configuration space, which is

read only. The purpose of this register is to allow the

PCI Maximum Latency value to be loaded from the se-

rial EEPROM.

The contents of this register are set to 18h when the

RST pin is asserted, before the serial EEPROM is

read, and after a serial EEPROM read error.

Table 64. MAX_LAT_A: PCI Maximum Latency Alias Register

0,1B*17B$ 3&,0LQLPXP *UDQW$OLDV5HJLVWHU

Offset 1B0h

This register is a writable alias of the Minimum Grant

field at offset 3Eh in PCI configuration space, which is

read only. The purpose of this register is to allow the

PCI Minimum Grant value to be loaded from the serial

EEPROM.

The contents of this register are set to 18h when the

RST pin is asserted, before the serial EEPROM is

read, and after a serial EEPROM read error.

Table 65. MIN_GNT_A: PCI Minimum Grant Alias Register

3$'5 3K\VLFDO $GGUHVV5HJLVWHU

Offset 160h

The contents of this register are cleared to 0 when the

RST pin is asserted. This register is not cleared by the

serial EEPROM read operation or by a serial EEPROM

read error.

Bit

Name

Description

7-0

MAX_LAT

Maximum Latency. Specifies the maximum arbitration latency the Am79C976 controller can

sustain without causing problems to the network activity. The register value specifies the time in

units of

1/4 microseconds. MAX_LAT is aliased to the PCI configuration space register

MAX_LAT (offset 3Fh). The host will use the value in the register to determine the setting of the

Am79C976 Latency Timer register.

The default value for MAX_LAT is 18h which corresponds to 6

ms.

This register is an alias of BCR22, bits [15:8] and of offset 3Fh in PCI configuration space.

Bit

Name

Description

7-0

MIN_GNT

Minimum Grant. Specifies the minimum length of a burst period the Am79C976 controller needs to

keep up with the network activity. The length of the burst period is calculated assuming a clock rate

of 33 MHz. The register value specifies the time in units of 1/4

ms. MIN_GNT is aliased to the PCI

configuration space register MIN_GNT (offset 3Eh). The host will use the value in the register to

determine the setting of the Am79C976 Latency Timer register.

The default value for MIN_GNT is 18h which corresponds to 6

ms.

This register is an alias of BCR22, bits [7:0] and of offset 3Eh in PCI configuration space.

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