AM79C974 datasheet(65/153 Pages) AMD

65 / 153 page

P R E L I M I N A R Y

AMD

Am79C974

Note that when I/O resource width is defined as 32 bits

(DWIO mode), the upper 16 bits of the I/O resource is

reserved and written as ZEROS and read as undefined,

except for the APROM locations and CSR88

. The

APROM locations and CSR88 are the only I/O re-

sources for which all 32 bits will have defined values.

However, this is true only when the Am79C974 control-

ler is in DWIO mode.

Configuring the Am79C974 controller for DWIO mode is

accomplished whenever there is any attempt to perform

a 32-bit write access to the RDP location (offset 10h).

See the DWIO section for more details.

Table 4 describes all possible bus slave accesses that

may be directed toward the Am79C974 controller. (i.e.,

the Am79C974 controller is the target device during the

transfer.) The first column indicates the type of slave ac-

cess. RD stands for READ, WR for a WRITE operation.

The second column indicates the value of the C/

BE[3:0]

lines during the data phase of the transfer. The four byte

columns (AD[31:24], AD[23:16], AD[15:8], AD[7:0]) in-

dicate the value on the address/data bus during the data

phase of the access. “data” indicates the position of the

active bytes; “copy” indicates the positions of copies of

the active bytes; “undef” indicates byte locations that are

undefined during the transfer.

Table 4. Bus Slave Accesses

TYPE

BE[3:0]

[31:24]

[23:16]

[15:8]

[7:0]

Comments

0000

data

DWORD access to DWORD address, e.g. 300h,

30Ch, 310h (DWIO mode only)

1100

undef

data

word access to even word address, e.g. 300h,

30Ch, 310h (WIO mode only)

0011

data

copy

word access to odd word address, e.g. 302h, 30Eh,

312h (WIO mode only)

1110

undef

data

byte access to lower byte of even word address, e.g.

300h, 304h (WIO mode only, APROM accesses

only)

1101

undef

data

undef

byte access to upper byte of even word address,

e.g. 301h, 305h (WIO mode only, APROM accesses

only)

1011

undef

data

undef

copy

byte access to lower byte of odd word address, e.g.

302h, 306h (WIO mode only, APROM accesses

only)

0111

data

undef

copy

undef

byte access to upper byte of odd word address, e.g.

303h, 307h (WIO mode only, APROM accesses

only)

0000

data

DWORD access to DWORD address, e.g. 300h,

30Ch, 310h (DWIO mode only)

1100

undef

data

word access to even word address, e.g. 300h,

30Ch, 310h (WIO mode only)

0011

data

undef

word access to odd word address, e.g. 302h, 30Eh,

312h (WIO mode only)

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