diff --git a/CDC1700/cdc1700_cd.c b/CDC1700/cdc1700_cd.c
index c30ae960..d50869d1 100644
--- a/CDC1700/cdc1700_cd.c
+++ b/CDC1700/cdc1700_cd.c
@@ -325,30 +325,14 @@ IO_DEVICE CDdev = IODEV(NULL, "1733-2", 1733, 3, 0xFF, 0,
 */
 
 UNIT cd_unit[] = {
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[0], &cd_unit[1]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[0], &cd_unit[0]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[1], &cd_unit[3]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[1], &cd_unit[2]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[2], &cd_unit[5]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[2], &cd_unit[4]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[3], &cd_unit[7]
-  },
-  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE),
-    0, 0, 0, 0, 0, &CDunits[3], &cd_unit[6]
-  }
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)},
+  { UDATA(&cd_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_856_4, CD856_4_SIZE)}
 };
 
 REG cd_reg[] = {
@@ -1058,7 +1042,27 @@ static t_stat CDreset(DEVICE *dptr)
 t_stat cd_reset(DEVICE *dptr)
 {
   t_stat r = SCPE_OK;
+  static t_bool Initialized = FALSE;
 
+  if (!Initialized) { /* Initialize additional UNIT state not done by UDATA macro */
+    Initialized = TRUE;
+    cd_unit[0].up7 = &CDunits[0];
+    cd_unit[0].up8 = &cd_unit[1];
+    cd_unit[1].up7 = &CDunits[0];
+    cd_unit[1].up8 = &cd_unit[0];
+    cd_unit[2].up7 = &CDunits[1];
+    cd_unit[2].up8 = &cd_unit[3];
+    cd_unit[3].up7 = &CDunits[1];
+    cd_unit[3].up8 = &cd_unit[2];
+    cd_unit[4].up7 = &CDunits[2];
+    cd_unit[4].up8 = &cd_unit[5];
+    cd_unit[5].up7 = &CDunits[2];
+    cd_unit[5].up8 = &cd_unit[4];
+    cd_unit[6].up7 = &CDunits[3];
+    cd_unit[6].up8 = &cd_unit[7];
+    cd_unit[7].up7 = &CDunits[3];
+    cd_unit[7].up8 = &cd_unit[6];
+  }
   if (IOFWinitialized)
     if ((dptr->flags & DEV_DIS) == 0)
       if ((r = checkReset(dptr, CDdev.iod_equip) == SCPE_OK)) {
diff --git a/CDC1700/cdc1700_dp.c b/CDC1700/cdc1700_dp.c
index 1e0aa491..face232c 100644
--- a/CDC1700/cdc1700_dp.c
+++ b/CDC1700/cdc1700_dp.c
@@ -249,12 +249,8 @@ IO_DEVICE DPdev = IODEV(NULL, "1738-B", 1738, 3, 0xFF, 0,
 */
 
 UNIT dp_unit[] = {
-  { UDATA(&dp_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_854, DP854_SIZE),
-    0, 0, 0, 0, 0, &DPunits[0]
-  },
-  { UDATA(&dp_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_854, DP854_SIZE),
-    0, 0, 0, 0, 0, &DPunits[1]
-  },
+  { UDATA(&dp_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_854, DP854_SIZE)},
+  { UDATA(&dp_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_854, DP854_SIZE)},
 };
 
 REG dp_reg[] = {
@@ -812,6 +808,8 @@ t_stat dp_reset(DEVICE *dptr)
 {
   t_stat r;
 
+  dp_unit[0].up7 = &DPunits[0];
+  dp_unit[1].up7 = &DPunits[1];
   if (IOFWinitialized)
     if ((dptr->flags & DEV_DIS) == 0)
       if ((r = checkReset(dptr, DPdev.iod_equip)) != SCPE_OK)
diff --git a/sim_defs.h b/sim_defs.h
index cec4d543..0b48e3f8 100644
--- a/sim_defs.h
+++ b/sim_defs.h
@@ -594,11 +594,6 @@ struct UNIT {
     void                (*io_flush)(UNIT *up);          /* io flush routine */
     uint32              iostarttime;                    /* I/O start time */
     int32               buf;                            /* buffer */
-    int32               wait;                           /* wait */
-    int32               u3;                             /* device specific */
-    int32               u4;                             /* device specific */
-    int32               u5;                             /* device specific */
-    int32               u6;                             /* device specific */
     void                *up7;                           /* device specific */
     void                *up8;                           /* device specific */
     uint16              us9;                            /* device specific */
@@ -631,6 +626,14 @@ struct UNIT {
     double              a_due_gtime;                    /* due time (in instructions) for timer event */
     double              a_usec_delay;                   /* time delay for timer event */
 #endif
+    /* Everything above here in the UNIT structure is within the scope of the UDATA 
+       macro initializer, if a simulator developer wants to initialize any of these 
+       values, they must be done by explicit code usually in a device reset routine */
+    int32               wait;                           /* wait */
+    int32               u3;                             /* device specific */
+    int32               u4;                             /* device specific */
+    int32               u5;                             /* device specific */
+    int32               u6;                             /* device specific */
     };
 
 /* Unit flags */
@@ -911,7 +914,12 @@ struct MEMFILE {
 
  */
 
-#define UDATA(act,fl,cap) NULL,act,NULL,NULL,NULL,NULL,0,0,(fl),0,(cap),0,NULL,0,0
+#ifdef SIM_ASYNCH_IO
+#define UDATA(act,fl,cap) NULL,act,NULL,NULL,NULL,NULL,0,0,(fl),0,(cap),0,NULL,0,0,NULL,NULL,0,0,NULL,NULL,NULL,0,0,0,NULL,0,NULL,NULL,0,NULL,\
+                          NULL,NULL,NULL,0,NULL,0,0,0,0,0
+#else
+#define UDATA(act,fl,cap) NULL,act,NULL,NULL,NULL,NULL,0,0,(fl),0,(cap),0,NULL,0,0,NULL,NULL,0,0,NULL,NULL,NULL,0,0,0,NULL,0,NULL,NULL,0,NULL
+#endif
 
 /* Register initialization macros.