dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 75

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

7 0 Signal Descriptions
7 3 MAC INDICATION INTERFACE
The MAC Indication Interface provides a delayed version of the byte stream presented to the Ring Engine at the PHY Indication
Interface Every byte of all incoming frames is presented at the MAC Indication Interface Every byte time (80 ns) one byte of
data with Odd parity is presented at the MAC Indication Interface This byte stream is interpreted by the system interface logic
using the control signals that are provided in parallel with the byte stream These control signals are used to determine frame
boundaries in the byte stream determine whether or not to (continue to) copy a frame and to provide status on received PDUs
In the following sections an overview of the signals is provided (Section 7 3 1) as well as a detailed explanation (Section 7 3 2)
with several example timing scenarios (Section 7 3 3)
7 3 1 Overview
The MAC Indication Interface is divided into one group of data signals and five groups of control signals
The data signals consist of the 8 bits of MAC Indicate Data (MID) with parity
The control signals consist of 5 groups
The PDU Sequencing signals are asserted at different points within a PDU
RCSTART when the Starting Delimiter is present on MID
FCRCVD
DARCVD
SARCVD
INFORCVD when the fourth byte of the info field is on MID until the next Starting Delimiter
Not all of the sequencing signals would be used in a typical implementation
The PDU Flags provide the input for potential copy criteria and status breakpoints The results of the comparisons between the
station’s long or short address and the frame’s source and destination addresses are provided in the AFLAG and MFLAG
signals The sequencing information is used to determine when this information is valid Since the Ring Engine is capable of
accomplishing four internal comparisons on any given frame two signals give the internal comparison that was accomplished
AFLAG
MFLAG
SAMESA
SAMEINFO First four bytes of Info same as in previous frame Valid with INFORCVD on MAC frames Can be used to inhibit
No temporary buffering is provided in the Ring Engine The system interface must provide this buffering while the decision is
made on whether or not to continue to copy the frame
Termination Event One of these signals is asserted at the end of every PDU
EDRCVD
TKRCVD
FRSTRP
FOERROR when the byte with the format error is on MID
MACRST





PDU Sequencing to aid in delimiting PDUs from the byte stream and sequencing through fields in the received PDUs
PDU Flags to aid in the decision of whether or not to continue to copy a PDU
Termination Event to determine when and how a PDU terminated
Termination Status to provide status on received frames
External Flags to allow external address comparison and copy information to be conveyed back to the Ring Engine
when the Ending Delimiter is on MID until the end of the Frame Status (typically asserted for two byte times)
when the Ending Delimiter of a token is on MID
when the first Idle byte of a stripped frame is on MID
when a MACRST occurs or Ring Engine in Stop Mode
when the Frame Control Field is on MID
when the last byte of the DA is on MID until the next Starting Delimiter
when the last byte of the SA is on MID until the next Starting Delimiter
Internal DA Match There are actually four AFLAGs as determined by the two signals FCSL Short Long DAIG
Individual Group Valid with DARCVD
Internal SA Match There are actually two MFLAGs as determined by the values of FCSL Valid with SARCVD
SA same as in previous frame Valid with SARCVD on Non-MAC frames Can be used by external logic to batch
status or reduce the number of interrupts when multiple frames are received from the same station
copying of identical MAC frames
(Continued)
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