AM79C975VCW datasheet(110/304 Pages) AMD

110 / 304 page

110

Am79C973/Am79C975

P R E L I M INARY

All I/O resources must be accessed in word quantities

and on word addresses. The Address PROM locations

can also be read in byte quantities. The only allowed

DWord operation is a write access to the RDP, which

switches the device to DWord I/O mode. A read access

other than listed in the table below will yield undefined

data, a write operation may cause unexpected repro-

gramming of the Am79C973/Am79C975 control regis-

ters. Table 21 shows legal I/O accesses in Word I/O

mode.

Double Word I/O Mode

The Am79C973/Am79C975 controller can be config-

ured to operate in DWord (32-bit) I/O mode. The soft-

ware can invoke the DWIO mode by performing a

DWord write access to the I/O location at offset 10h

(RDP). The data of the write access must be such that

it does not affect the intended operation of the

Am79C973/Am79C975 controller. Setting the device

into 32-bit I/O mode is usually the first operation after

H_RESET or S_RESET. The RAP register will point to

CSR0 at that time. Writing a value of 0 to CSR0 is a

safe operation. DWIO (BCR18, bit 7) will be set to 1 as

an indication that the Am79C973/Am79C975 controller

operates in 32-bit I/O mode.

Note: Even though the I/O resource mapping changes

when the I/O mode setting changes, the RDP location

offset is the same for both modes. Once the DWIO bit

has been set to 1, only H_RESET can clear it to 0. The

DWIO mode setting is unaffected by S_RESET or set-

ting of the STOP bit. Table 22 shows how the 32 bytes

of address space are used in DWord I/O mode.

All I/O resources must be accessed in DWord quanti-

ties and on DWord addresses. A read access other

than listed in Table 23 will yield undefined data, a write

operation may cause unexpected reprogramming of

the Am79C973/Am79C975 control registers.

Table 20. I/O Map In Word I/O Mode (DWIO = 0)

Offset

No. of

Bytes

00h - 0Fh

APROM

10h

RDP

12h

RAP (shared by RDP and BDP)

14h

Reset Register

16h

BDP

18h - 1Fh

Reserved

AM79C975VCW Datasheet(PDF) 110 Page - Advanced Micro Devices

AM79C975VCW Datasheet(HTML) 110 Page - Advanced Micro Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL