dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 64

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

6 0 Control Information
Lost Frame Counter (LFCT)
The Lost Frame Counter (LFCT) is specified in the FDDI MAC Standard It is the count of all instances where a Format Error is
detected in a frame or token such that the credibility of the PDU reception is in doubt
The Lost Frame Counter is incremented when any symbol other than a data or Idle symbol is received between the Starting and
Ending Delimiters of a PDU (this includes parity errors)
Interrupts are available on increment (CILR FRLST) and when the 20-bit counter overflows and wraps around (COLR FRLST)
ACCESS RULES
In REV 1 of the BMAC device the Lost Count includes frames stripped on an ODD symbol boundary This may cause larger than
expected counts in Rings where an upstream station produces valid remnants that begin on an ODD symbol boundary (The
Ring Engine converts these remnants to byte aligned remnants so that only the downstream station would increment its Lost
Count ) In subsequent revisions remnants that begin on an odd symbol boundary are not considered lost frames and do not
cause the Lost Count to increment
LFCT0
LFCT1
LFCT2
LFCT3
Address
A8 – ABh
CT(15)
CT(7)
Zero
Zero
D7
Always
Read
CT(14)
CT(6)
Zero
Zero
D6
(Continued)
Stop Mode
Write
CT(13)
CT(5)
Zero
Zero
D5
CT(12)
CT(4)
Zero
Zero
D4
64
CT(19)
CT(11)
CT(3)
Zero
D3
CT(18)
CT(10)
CT(2)
Zero
D2
CT(17)
CT(9)
CT(1)
Zero
D1
CT(16)
CT(8)
CT(0)
Zero
D0