AM79C987 AMD [Advanced Micro Devices], AM79C987 Datasheet - Page 9

• Manufacturer Part Number: AM79C987
• Description: Hardware Implemented Management Information Base (HIMIB) Device
• Manufacturer: AMD [Advanced Micro Devices]

C/D = 1
C/D = 0
An exception to the normal Command/Data Port access
scheme, is the Status Register which is read directly by
reading only the C Port. This allows the Status Register
to be read directly, without the need to write to the
C Port.
Register Definition
In the following description, all bit fields are ordered
such that the left most bit is the most significant bit. Un-
used Port and Register Numbers are reserved and
should not be accessed as this may cause device mal-
function.
When specifying the Port or Bank Number, the following
command byte is written to the C Port:
C Port Write
P[4:0] represent the Register Bank or Port Number.
These are organized as follows:
P = [P4P3P2P1P0]
Note that to access the P register the three most signifi-
cant bits of this byte must be zero.
MSB
0
AMD
0
Command (C) Port
0
Data (D) Port
P4
P3
Figure 1. Overview of HIMIB Register Definition
P2
P1
P R E L I M I N A R Y
000XXXXX
111XXXXX
Register (R) Register
P0
LSB
Port (P) Register
Am79C987
When specifying the Register or Attribute to be ac-
cessed, the following command byte is written to the
C Port.
C Port Write
R = [R4R3R2R1R0]
Note that to access the R register the three most signifi-
cant bits of this byte must be one.
MSB
1
16 – 23
P [4:0]
31
0
1
2
1
Port (or Bank)
Pointer
Register (or Attribute)
Pointer
1
Port/Register Bank
Repeater Registers
Port Status Registers
Port Control Registers
Twisted Pair Ports Attributes
AUI Port Attributes
R4
R3
Bank 31
Bank 1
Bank 0
R2
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
.
R1
0
Register
31
0
Register
31
0
Register
31
17305B-4
R0
LSB
9