dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 19

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

5 0 Functional Description
5 5 FRAME STATUS PROCESSING
Each frame contains three or more Control Indicators The
FDDI Standard specifies three the E A and C Indicators
When a frame is transmitted the Control Indicators are
transmitted as R (Reset) symbols If an error is detected by
a station that receives the frame the E Indicator is changed
to an S (Set) symbol If a station recognizes the DA of a
frame as its own address (Individual Group or Broadcast)
the A Indicator is changed to an S symbol If that station
then copies the frame the C Indicator is changed to an S
symbol
E Flag is set when the local FCS check fails or when the E Indicator is received as anything other than R
A Flag is the internal
The Copy Flag is a one cycle delayed version of the VCOPY input
N Flag indicates that an NSA frame is being received This signal is sampled at the same time that the received A indicator is being investigated
X Represents a Don’t Care Condition
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
E
X
X
X
X
X
Received Indicators
A
R
R
R
R
R
R
R
R
R
R
R
R
S
S
S
S
S
S
S
S
S
S
S
Flag or the external A Flag (pin EA) when Option Emind is set
C
R
R
R
R
S
S
S
S
R
R
R
R
S
S
T
T
T
T
T
T
T
T
T
TABLE 5-5 Control Indicators Processing
(Continued)
E
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
0
1
0
0
0
0
1
A
0
1
1
X
0
1
1
X
X
X
1
0
X
X
0
1
1
X
1
0
1
1
X
Flags
19
Copy
The received value of the Control Indicators for every frame
received is reported at the MAC Indicate Interface on sig-
nals MID(7 – 0) On a frame transmitted by this station the
returning Control Indicators give the transmission status
The Ending Delimiter followed by the Frame Status Indica-
tors should begin and end on byte boundaries Control Indi-
cators are repeated until the first non R S or T is received
The processing of properly aligned E A and C indicators by
the Ring Engine is detailed in Table 5-5 Given the shown
received Control Indicator values and the settings of the
internal flags the noted control indicator values will be
transmitted
X
X
X
X
X
X
X
X
X
X
X
X
0
1
0
1
0
1
0
1
1
0
1
N
X
X
X
X
X
X
X
X
1
0
0
X
X
X
X
X
X
X
0
X
X
1
X
E
R
R
R
S
R
R
R
S
R
R
R
R
R
S
R
R
R
S
R
R
R
R
S
Transmitted Indicators
A
R
R
R
R
R
R
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
C
R
R
R
R
R
R
S
R
R
R
R
S
S
S
S
S
S
T
S
T
S
T
T