PDP18B: Latest updates from Bob Supnik

- Added unix v0 terminal support
- Added 3-cycle databreak set/show entries
- Revised for dynamically allocated memory
- Added support for -u modifier (UC15 and Unix v0)

These changes are to support the Unix v0 bringup and to implement a
"Unix input" mode on the console terminal.  In Unix mode, CR and LF are
swapped (so that a modern terminal can use 'enter' instead of CTRK-J to
create the newline Unix expects), escape is mapped to altmode (175),
upper and lower case are enabled and the parity bit is forced to 1.  This
most closely matches the characteristics of the KSR-37, but there is no
definitive evidence of the terminal that was actually used.

PDP18B/pdp18b_defs.h

@@ -23,6 +23,7 @@
    used in advertising or otherwise to promote the sale, use or other dealings
    in this Software without prior written authorization from Robert M Supnik.
 
+   10-Mar-16    RMS     Added 3-cycle databreak set/show routines
    26-Feb-16    RMS     Added RB09 to PDP-7 for Unix "v0" and RM09 to PDP-9
    13-Sep-15    RMS     Added DR15C
    18-Apr-12    RMS     Added clk_cosched prototype
@@ -104,6 +105,7 @@
                                         TC59D magnetic tape
                                         TC15/TU56 DECtape
                                         LT15/LT19 additional Teletypes
+					DR15C parallel interface to UC15
 
    ??Indicates not implemented.  The PDP-4 manual refers to a memory
    ??extension control; there is no documentation on it.
@@ -160,7 +162,6 @@
 #define MTA             0                               /* magtape */
 #define TC02            0                               /* DECtape */
 #define TTY1            16                              /* second Teletype(s) */
-#define DR              0                               /* DR15C */
 #define BRMASK          0377400                         /* bounds mask */
 #define BRMASK_XVM      0777400                         /* bounds mask, XVM */
 #endif
@@ -516,6 +517,8 @@ typedef struct {
 
 t_stat set_devno (UNIT *uptr, int32 val, char *cptr, void *desc);
 t_stat show_devno (FILE *st, UNIT *uptr, int32 val, void *desc);
+t_stat set_3cyc_reg (UNIT *uptr, int32 val, char *cptr, void *desc);
+t_stat show_3cyc_reg (FILE *st, UNIT *uptr, int32 val, void *desc);
 
 int32 clk_cosched (int32 wait);