B-6700 WORDS


       B U R R O U G H S   6 7 0 0 :     W O R D   S T R U C T U R E
       I N   M A N U A L S   A N D   O N   L A M P S   D I S P L A Y


  +----+    +----+----+----+----+----+----+----+----+----+----+----+----+
  | 51 |    | 47 | 43 | 39 | 35 | 31 | 27 | 23 | 19 | 15 | 11 | 07 | 03 |
  +----+    +----+----+----+----+----+----+----+----+----+----+----+----+
  | 50 |    | 46 | 42 | 38 | 34 | 30 | 26 | 22 | 18 | 14 | 10 | 06 | 02 |
  +----+    +----+----+----+----+----+----+----+----+----+----+----+----+
  | 49 |    | 45 | 41 | 37 | 33 | 29 | 25 | 21 | 17 | 13 | 09 | 05 | 01 |
  +----+    +----+----+----+----+----+----+----+----+----+----+----+----+
  | 48 |    | 44 | 40 | 36 | 32 | 28 | 24 | 20 | 16 | 12 | 08 | 04 | 00 |
  +----+    +----+----+----+----+----+----+----+----+----+----+----+----+


  Bit 51  =  Parity bit for odd parity; checked and set by hardware
  Bit 50 + 49 + 48  =  Tag
  Bit 47 - 00  =  Actual information
       Bit 47  =  Most significant bit
       Bit 00  =  Least significant bit


  Tag bits   Meaning of the actual information         Number of words
  50 49 48   ---------------------------------         in memory fetch
  --------                                             ---------------
  0  1  0    Double-word data (same tag in both words)    2
  0  0  0    Single-word data and strings                1
  1  0  1    Descriptor, for Strings and Data            1
  0  0  1    Indirect reference, Normal and Stuffed      1
  0  1  1    Mark stack control                          1
  1  1  1    Program control                             1
  0  1  1    Return control                              1
  1  0  0    Step index                                  1


  In the descriptor (tag = 101) the meaning of the bits 42,41,40 is:

  Word bits  Type of addressed information
  42 41 40   -----------------------------
  --------
  0  0  1    Double word data
  0  0  0    Single word data
  1  0  0    Single word string with 6 bytes of 8 bits
  0  1  1    Single word string with 8 fields of 6 bits
  0  1  0    Single word string with 12 nibbles of 4 bits

Return to description about Unisys computers