diff --git a/VAX/vax820_defs.h b/VAX/vax820_defs.h
index 91b1e78b..cc87d6c4 100644
--- a/VAX/vax820_defs.h
+++ b/VAX/vax820_defs.h
@@ -332,6 +332,7 @@ typedef struct {
 #define INT_V_DUPTX     12
 #define INT_V_RK        13
 #define INT_V_CH        14
+#define INT_V_UW        15
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -366,6 +367,7 @@ typedef struct {
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
 #define INT_CH          (1u << INT_V_CH)
+#define INT_UW          (1u << INT_V_UW)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -391,6 +393,7 @@ typedef struct {
 #define IPL_RK          (0x15 - IPL_HMIN)
 #define IPL_TDRX        (0x14 - IPL_HMIN)
 #define IPL_TDTX        (0x14 - IPL_HMIN)
+#define IPL_UW          (0x15 - IPL_HMIN)
 
 /* Device vectors */
 
diff --git a/VAX/vax820_syslist.c b/VAX/vax820_syslist.c
index 6d8f37ea..879a73be 100644
--- a/VAX/vax820_syslist.c
+++ b/VAX/vax820_syslist.c
@@ -62,6 +62,7 @@ extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
 extern DEVICE dup_dev;
 extern DEVICE ch_dev;
+extern DEVICE uw_dev;
 
 extern UNIT cpu_unit;
 extern void WriteB (uint32 pa, int32 val);
@@ -103,6 +104,7 @@ DEVICE *sim_devices[] = {
     &dmc_dev,
     &dup_dev,
     &ch_dev,
+    &uw_dev,
     NULL
     };
 
diff --git a/VAX/vax860_defs.h b/VAX/vax860_defs.h
index d3570ace..860435e0 100644
--- a/VAX/vax860_defs.h
+++ b/VAX/vax860_defs.h
@@ -371,6 +371,7 @@ typedef struct {
 #define INT_V_DUPTX     12
 #define INT_V_RK        13
 #define INT_V_CH        14
+#define INT_V_UW        15
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -405,6 +406,7 @@ typedef struct {
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
 #define INT_CH          (1u << INT_V_CH)
+#define INT_UW          (1u << INT_V_UW)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -430,6 +432,7 @@ typedef struct {
 #define IPL_RK          (0x15 - IPL_HMIN)
 #define IPL_TDRX        (0x14 - IPL_HMIN)
 #define IPL_TDTX        (0x14 - IPL_HMIN)
+#define IPL_UW          (0x15 - IPL_HMIN)
 
 /* Device vectors */
 
diff --git a/VAX/vax860_syslist.c b/VAX/vax860_syslist.c
index 6722b38d..6058a01e 100644
--- a/VAX/vax860_syslist.c
+++ b/VAX/vax860_syslist.c
@@ -66,6 +66,7 @@ extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
 extern DEVICE dup_dev;
 extern DEVICE ch_dev;
+extern DEVICE uw_dev;
 
 DEVICE *sim_devices[] = { 
     &cpu_dev,
@@ -105,6 +106,7 @@ DEVICE *sim_devices[] = {
     &dmc_dev,
     &dup_dev,
     &ch_dev,
+    &uw_dev,
     NULL
     };
 
diff --git a/Visual Studio Projects/VAX8200.vcproj b/Visual Studio Projects/VAX8200.vcproj
index d004bfce..91cfff08 100644
--- a/Visual Studio Projects/VAX8200.vcproj	
+++ b/Visual Studio Projects/VAX8200.vcproj	
@@ -397,6 +397,10 @@
 				RelativePath="..\VAX\vax_syscm.c"
 				>
 			</File>
+			<File
+				RelativePath="..\VAX\vax_uw.c"
+				>
+			</File>
 			<File
 				RelativePath="..\VAX\vax_watch.c"
 				>
diff --git a/Visual Studio Projects/VAX8600.vcproj b/Visual Studio Projects/VAX8600.vcproj
index a534a8e3..2e03a27d 100644
--- a/Visual Studio Projects/VAX8600.vcproj	
+++ b/Visual Studio Projects/VAX8600.vcproj	
@@ -413,6 +413,10 @@
 				RelativePath="..\VAX\vax_syscm.c"
 				>
 			</File>
+			<File
+				RelativePath="..\VAX\vax_uw.c"
+				>
+			</File>
 			<Filter
 				Name="slirp"
 				>
diff --git a/makefile b/makefile
index 65587bbc..90d269d3 100644
--- a/makefile
+++ b/makefile
@@ -1829,7 +1829,7 @@ VAX8200 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${VAXD}/vax_mmu.c ${VAXD}/vax_sys.c  ${VAXD}/vax_syscm.c \
 	${VAXD}/vax_watch.c ${VAXD}/vax820_stddev.c ${VAXD}/vax820_bi.c \
 	${VAXD}/vax820_mem.c ${VAXD}/vax820_uba.c ${VAXD}/vax820_ka.c \
-	${VAXD}/vax820_syslist.c \
+	${VAXD}/vax_uw.c ${VAXD}/vax820_syslist.c \
 	${PDP11D}/pdp11_rl.c ${PDP11D}/pdp11_rq.c ${PDP11D}/pdp11_ts.c \
 	${PDP11D}/pdp11_dz.c ${PDP11D}/pdp11_lp.c ${PDP11D}/pdp11_tq.c \
 	${PDP11D}/pdp11_xu.c ${PDP11D}/pdp11_ry.c ${PDP11D}/pdp11_cr.c \
@@ -1845,7 +1845,7 @@ VAX8600 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${VAXD}/vax_mmu.c ${VAXD}/vax_sys.c  ${VAXD}/vax_syscm.c \
 	${VAXD}/vax860_stddev.c ${VAXD}/vax860_sbia.c \
 	${VAXD}/vax860_abus.c ${VAXD}/vax780_uba.c ${VAXD}/vax7x0_mba.c \
-	${VAXD}/vax860_syslist.c \
+	${VAXD}/vax_uw.c ${VAXD}/vax860_syslist.c \
 	${PDP11D}/pdp11_rl.c ${PDP11D}/pdp11_rq.c ${PDP11D}/pdp11_ts.c \
 	${PDP11D}/pdp11_dz.c ${PDP11D}/pdp11_lp.c ${PDP11D}/pdp11_tq.c \
 	${PDP11D}/pdp11_xu.c ${PDP11D}/pdp11_ry.c ${PDP11D}/pdp11_cr.c \