DP83266VF National Semiconductor, DP83266VF Datasheet - Page 15

• Manufacturer Part Number: DP83266VF
• Description: IC MEDIA ACSS CTRL INTF 160PQFP
• Manufacturer: National Semiconductor

Specifications of DP83266VF

• Applications: *
• Voltage - Supply: 4.75 V ~ 5.25 V
• Package / Case: 160-BFQFP
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Other names: *DP83266VF

4 0 FDDI MAC Facilities
Frames Generated Externally
The Ring Engine transmits frames passed to it from the Sys-
tem Interface The data portion of the frame is created by
the System Interface The data portion begins with the FC
field and ends with the last byte of the INFO field The FC
field is passed transparently to the ring The length bit in the
FC field is used to determine the length of the transmitted
addresses The data is passed as a byte stream across the
MAC Request Interface as shown in Table 4-5
Before the frame is transmitted the Ring Engine inserts the
Start of Frame Sequence with at least 8 bytes of Preamble
but no more than 40 bytes of Preamble The starting delimi-
ter is transmitted as a JK symbol pair The Source Address
is normally transmitted by the Ring Engine since it uses the
Source Address to determine when to strip a frame from the
ring This can be overridden by using the Source Address
transparency capability Similarly the Frame Check Se-
quence (4 bytes) is normally transmitted by the Ring Engine
This can be overridden with the FCS transparency capabili-
ty With FCS transparency the FCS is transmitted from the
data stream The End of Frame Sequence is always trans-
mitted by the Ring Engine as TR RR
Frames Generated by Ring Engine
The Ring Engine generates and detects several frames in
order to attain and maintain an operational ring
INFO
Field
FCS
PA
SD
FC
DA
SA
ED
FS
4 if present
t
(bytes)
2 or 6
2 or 6
8
Size
t
1
1
1
1
s
TABLE 4-5 Frame Formats
0
40
MA Request
INFO
FCS
FC
DA
SA
(Continued)
MSA MLA or SA
PH Request
Idle Pairs
INFO
FCS
DA
RR
FC
TR
JK
15
Void Frames
Void frames are used during normal operation The Ring
Engine generates two types of void frames regular Void
frames and My Void frames
If Short addressing is enabled Void frames with the short
address (MSA) are transmitted Otherwise Void frames with
the long address (MLA) are transmitted Table 4-6 shows
the Void frame format
Void frames are transmitted in order to reset the Valid
Transmission timers (TVX) in other stations to eliminate un-
necessary entry to the Claim state Stations are not required
to copy Void frames Void frames are transmitted by the
Ring Engine in two situations
1 While holding a token when no data is ready to be trans-
2 After a frame transmission is aborted
My Void frames are transmitted by the Ring Engine in
three situations
1 After a request to measure the Ring Latency has been
2 After this station wins the Claim process and before the
3 After a frame has been transmitted with the STRIP op-
Void frames are also detected by the Ring Engine A Void
frame with a Source Address other than MSA or MLA is
considered an Other Void frame
Claim Frames
Claim frames are generated continuously with minimum pre-
amble while the Ring Engine is in the Transmit Claim state
The format of Claim frames generated by the Ring Engine is
shown in Table 4-7 When long addressing is enabled
frames with the long address (MLA) are transmitted Other-
wise frames with the short address (MSA) are transmitted
The Ring Engine detects reception of valid Claim frames A
comparison is performed between the first four bytes of the
received INFO field and the value of TREQ programmed in
the parameter RAM in order to distinguish Higher Claim
Lower Claim Duplicate Claim and My Claim
Beacon Frames
Beacon frames are transmitted continuously with minimum
preamble when the Ring Engine is in the Transmit Beacon
state The format of Beacon frames generated by the Ring
Engine is shown in Table 4-8 When long addressing is en-
abled frames with the long address (MLA) are transmitted
Otherwise frames with the short address (MSA) are trans-
mitted
mitted
made and the next early token is captured
token is issued
tion and before the token for that service opportunity is
issued