AM79C976 datasheet(111/309 Pages) AMD

111 / 309 page

8/01/00

Am79C976

111

P R E L I M INARY

USER ACCESSIBLE REGISTERS

The Am79C976 controller has four types of user regis-

ters: the PCI configuration registers, the memory-

mapped registers, the Control and Status registers

(CSRs), and the Bus Control registers (BCRs). The

CSRs and BCRs are included for software compatibility

with older PCnet family devices. However, all CSR and

BCR functions can be accessed more efficiently

through the memory-mapped registers. Software writ-

ten for the Am79C976 device and future PCnet family

devices does not have to access any CSR or BCR.

The Am79C976 controller implements all PCnet-ISA

(Am79C960) registers, all C-LANCE (Am79C90) regis-

ters, all PCnet-FAST (Am79C971) registers, plus a

number of additional registers. The Am79C976 CSRs

are compatible upon power up with both the PCnet-ISA

CSRs and all of the C-LANCE CSRs.

The PCI configuration registers and the memory-

mapped registers can be accessed in any data width.

The CSRs and BCRs must be accessed according to

the I/O mode that is currently selected. When WIO

mode is selected, all CSR and BCR locations are de-

fined to be 16 bits in width. When DWIO mode is se-

lected, all these register locations are defined to be 32

bits in width, with the upper 16 bits of most register lo-

cations marked as reserved locations with undefined

values. When performing register write operations in

DWIO mode, the upper 16 bits should always be written

as zeros. When performing register read operations in

DWIO mode, the upper 16 bits of I/O resources should

always be regarded as having undefined values, ex-

cept for CSR88.

The Am79C976 controller’s registers can be divided

into several functional groups: PCI Configuration Alias

registers, PCI Configuration registers, Setup registers,

Running registers, and Test registers.

The PCI Configuration Alias registers are typically pro-

grammed through the EEPROM read operation. In this

way, they are initialized before the BIOS accesses the

PCI Configuration registers. This group includes the

MAX_LAT_A, MIN_GNT_A, PCIDATA0 - 7, PMC_A,

SID_A, SV ID _A a nd V I D_A regi sters and th e

ROM_CFG register.

The PCI Configuration registers are accessed by the

system BIOS software to configure the Am79C976

controller. These registers include the Memory Base

Address register, the Expansion ROM Base Address

Typically, device information will also be read from the

SID, SVID and VID registers.

The Setup registers include most of the remaining

memory mapped registers. The programming of these

is typically divided between the EEPROM and the

driver software. Many of these registers are optional

and need not be initialized unless the associated func-

tion is used.

Typically, the SRAM_SIZE, SRAM_BND and PADR

registers are initialized from the EEPROM. The driver

initializes the BADR, BADX, RCV_RING_LEN,

XMT_RING_LEN and LADRF registers. The CMD2,

CMD3, CTRL0, CTRL1 and CTRL2 registers are typi-

cally partially initialized from the EEPROM and partially

by the driver. The CMD7 and CTRL3 registers are ini-

ti al ized b y th e d r iv er. T h e d r iv er r e a d s th e

MIB_OFFSET and CHIPID registers at initialization

time. The PHY_ACCESS register may be used at this

time to initialize the external PHY.

Running registers are accessed by the driver software.

These include the CMD0, INT0, INTEN0, STAT0,

LADRF and MIB registers. The driver may access other

registers during operation depending on the features

being used.

PCI Configuration Registers

3&,9HQGRU,'5HJLVWHU

Offset 00h

The PCI Vendor ID register is a 16-bit register that iden-

tifies the manufacturer of the Am79C976 controller.

AMD’s Vendor ID is 1022h. Note that this vendor ID is

not the same as the Manufacturer ID in CSR88 and

CSR89. The vendor ID is assigned by the PCI Special

Interest Group.

The PCI Vendor ID register is read only.

This register is the same as BCR35, which can be writ-

ten by the EEPROM.

3&,'HYLFH ,'5HJLVWHU

Offset 02h

The PCI Device ID register is a 16-bit register that

uniquely identifies the Am79C976 controller within

AMD's product line. The Am79C976 Device ID is

2000h. Note that this Device ID is not the same as the

Part number in CSR88 and CSR89. The Device ID is

assigned by AMD. The Device ID is the same as the

PC net -P CI I I ( Am 79C9 7 0 A) an d P C ne t- FAS T

(Am79C971) devices.

The PCI Device ID register is read only.

3&,&RPPDQG5HJLVWHU

Offset 04h

The PCI Command register is a 16-bit register used to

control the gross functionality of the Am79C976 con-

troller. It controls the Am79C976 controller's ability to

generate and respond to PCI bus cycles. To logically

disconnect the Am79C976 device from all PCI bus cy-

cles except configuration cycles, a value of 0 should be

written to this register.

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