dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 53

• Manufacturer Part Number: dp83261
• Description: Bmac Device Fddi Media Access Controller
• Manufacturer: National Semiconductor Corporation

6 0 Control Information
Group Short Address
Group Short Address (GSA0) represents the station’s short 16-bit address bit GSA(15) to bit GSA(8)
It is possible to disable Short Group Addressing by programming bits GSA(14 – 8) to all Ones
ACCESS RULES
Design Note GSA(15) is not used in the comparison since the comparison will only be accomplished if the received DA(15) is a One
Fixed Group Address MAP (FGM0 – FGM1)
If the first 44 bits of a long DA DA(47 – 4) or if the first 12 bits of a short DA DA(15 – 4) are 1 the last 4 bits of the DA DA(3 – 0)
are used as an index into FGM
The 4-bit index into FGM can be viewed in two different ways It can be viewed as 4 bits selecting one of 16 bits where the
hexidecimal equivalent of DA(3 – 0) can be used as the index For example the broadcast address would index FGM(F) Alterna-
tively it can be viewed as one bit DA(3) selecting the byte (FGM0 or FGM1) and three bits DA(2 – 0) selecting one of 8 bits
within a byte
ACCESS RULES
Note Bit FGM(F) must be set to One to ensure proper handling of frames with the Universal Broadcast address including the SMT NSA frames This is mandatory
for interoperability on an FDDI Ring
GSA4
FGM0
FGM1
Address
Address
58 – 59h
4Eh
GSA(15)
FGM(7)
FGM(F)
D7
D7
Stop Mode
Stop Mode
Read
Read
GSA(14)
FGM(E)
FGM(6)
D6
D6
(Continued)
Stop Mode
Stop Mode
FGM(D)
GSA(13)
FGM(5)
Write
Write
D5
D5
FGM(4)
FGM(C)
GSA(12)
D4
D4
53
FGM(3)
FGM(B)
GSA(11)
D3
D3
FGM(A)
FGM(2)
GSA(10)
D2
D2
FGM(1)
FGM(9)
GSA(9)
D1
D1
FGM(0)
FGM(8)
GSA(8)
D0
D0