19-Sep-03
GENERATING BUSY AND ERROR FROM DAUGHTERBOARDS


DB <--> BC Communication Lines
==============================
             Specified   Current        New
MB J4*  Pin  BC Name     BC Name        BC Name        Active
--------------------------------------------------------------
SPARE0  26   DB_L3_DATA  DB_L3_DATA-i   DB_L3_DATA-i   hi
SPARE1  30   BC_BUSY     BC_BUSY   -o   unused    -o   --
SPARE2  34   L1_ERROR    unused    -i   DB_Error  -i   bit-stream
SPARE3  38   L1_BUSY     unconnected
SPARE4  42   L2_ERROR    unconnected
SPARE5  46   L2_BUSY     unconnected
--------------------------------------------------------------
* MB connector J4 called J3 on BC
-i = input to BC
-o = output from BC


GENERAL SIGNAL SPECIFICATIONS
=============================

DB_L3_DATA
----------
o Usage: set by DB to indicate that DB has a complete L3 event ready
  to transfer 
o Cleared: cleared by DB after PCI burst read of DB data begins

Bit stream for Busy/Error requests (DB_Error)
----------------------------------
o We can't use line SPARE1 as a BC input
  - wired as a BC output at Line-Driver/Buffer
o Need to encode Busy and Error Signals on one line (SPARE2)
  - copy 7-bit encoding scheme from TFC
  - L1Busy_On[]  = B"0001011"   Set L1Busy from DB
  - L1Busy_Off[] = B"0010011"   Reset L1Busy from DB
  - sclinit[]    = B"0100011"   Request SCL Init from DB (L1Error)
o For those DB's not sending Busy or Error to the BC (FRC & STC)
  - DB_Error line should be set to GND

DB_Busy (L1Busy_on/L1Busy_Off)
-------
o Usage: set by DB to request FRC to raise L1BUSY to the SCL hub.
  - Note: Dan Edmunds claims that the time between when a geographic
    sector raises L1BUSY and when L1Accepts stop should be within a
    single 132 ns tick, although it may take slightly longer.
  - in current scheme there is a total of 9 33M clocks of latency on
    this signal
o Cleared: cleared by DB after its internal busy condition goes away.
  - this is done by DB sending L1Busy_Off bit stream

DB_Error (sclinit)
--------
o Usage: set by DB to indicate that it is in an error state requiring
  an SCL Init.
o Cleared: cleared by DB at start of SCL Init sequence.
  - the BC clears its DB_Error state as part of its SCL Init sequence
  - the DB is *not* required to send a "Clear Error" signal to the BC