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Annotation of researchv10dc/vol2/Ucds/macro, revision 1.1

1.1     ! root        1: .NH
        !             2: Signal Bundles and Macros.
        !             3: .LP
        !             4: Consider this buffer between two 8-bit busses:
        !             5: .PS <fig1.pic
        !             6: It illustrates several
        !             7: .I jraw
        !             8: conventions.  The
        !             9: .I chip
        !            10: is indicated by a box; its
        !            11: .I name
        !            12: is
        !            13: .CW buffer ;
        !            14: its
        !            15: .I type
        !            16: is
        !            17: .CW 74F244 .
        !            18: These are simply unattached text strings that appear stacked inside the
        !            19: box.
        !            20: .I "Pin names"
        !            21: (e.g.,
        !            22: .CW D0 )
        !            23: are strings that appear on the inside edge of the box.
        !            24: .I Nets
        !            25: are lines that end on a pin.
        !            26: .I "Net names"
        !            27: are strings that are placed on nets.  A trailing
        !            28: .CW "-"
        !            29: conventionally indicates an active-low signal.
        !            30: .LP
        !            31: Even this trivial example involves repeated patterns.
        !            32: A much more succint equivalent is:
        !            33: .PS <fig2.pic
        !            34: The
        !            35: .I generator
        !            36: .CW "x<0:7>"
        !            37: expands into the ordered list
        !            38: .CW x0 ,
        !            39: .CW x1 ,...
        !            40: .CW x7 .
        !            41: The
        !            42: .I pattern
        !            43: .CW "D?\&"
        !            44: matches two-character pin names that begin with
        !            45: .CW D .
        !            46: (The space of possible names comes from the
        !            47: .CW .pins
        !            48: file entry for the chip type.)
        !            49: The names that match the pattern are
        !            50: .I "sorted alphabetically"
        !            51: and put into correspondance with the nets.
        !            52: .LP
        !            53: If connected sets of nets and pins do not have the same cardinality,
        !            54: the smaller set is reused until the larger is exhausted.  Thus in the
        !            55: example, the
        !            56: .CW drive-
        !            57: net gets connected to both
        !            58: .CW OE0-
        !            59: and
        !            60: .CW OE1- ,
        !            61: as desired.
        !            62: .LP
        !            63: Frequently one has a group of chips that will be used or replicated as
        !            64: a unit.  In such a case it makes sense to define a
        !            65: .I macro
        !            66: that may be instantiated as required.  A macro lives in its own file.
        !            67: Here is an example,
        !            68: .CW opm.j :
        !            69: .PS <opm.pic
        !            70: The dotted box (produced by selecting
        !            71: .CW macro
        !            72: in
        !            73: .I jraw ")"
        !            74: identifies the circuit as a macro.  Strings outside of this box
        !            75: (conventionally in upper case) are ``pin names'' visible to the
        !            76: outside world.  Most names inside the box will be made local to
        !            77: each instantiation.  Net names beginning with
        !            78: .CW "/"
        !            79: are ``globals,'' i.e., they represent the same signal throughout
        !            80: the design.
        !            81: .CW "/VCC"
        !            82: and
        !            83: .CW "/GND"
        !            84: are the most common global signals.
        !            85: .LP
        !            86: Now we use generators to make several instances of
        !            87: .CW opm.j :
        !            88: .PS <opmcall.pic
        !            89: Sixteen copies of the
        !            90: .CW opm
        !            91: circuit are made.  The pattern
        !            92: .CW "D?\&"
        !            93: is at a lower, i.e., ``faster running,'' level than
        !            94: .CW "opm<00:15>" ,
        !            95: with the effect that all the
        !            96: .CW D0 "'s"
        !            97: are connected to
        !            98: .CW "bd0" ,
        !            99: all the
        !           100: .CW D1 "'s"
        !           101: are connected to
        !           102: .CW "bd1" ,
        !           103: etc; similarly, all the
        !           104: .CW A0 "'s"
        !           105: are connected to
        !           106: .CW ba0 .
        !           107: On the other hand, all the
        !           108: .CW "CS-" "'s"
        !           109: are separate:
        !           110: .CW "opm00/CS-"
        !           111: (the instance of
        !           112: .CW CS-
        !           113: in
        !           114: .CW opm00 )
        !           115: is connected to
        !           116: .CW "ops00-" ,
        !           117: .CW "opm01/CS-"
        !           118: is connected to
        !           119: .CW "ops01-" ,
        !           120: etc.  The manual entries for
        !           121: .I cdm
        !           122: and
        !           123: .I cdmglob
        !           124: should be consulted for all the details.

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