diff --git a/doc/simh.doc b/doc/simh.doc
index 39984895..713fe58b 100644
Binary files a/doc/simh.doc and b/doc/simh.doc differ
diff --git a/scp.c b/scp.c
index 965fe2a7..da7c83fc 100644
--- a/scp.c
+++ b/scp.c
@@ -6504,8 +6504,9 @@ if (!(flag & EX_E))
 GET_RADIX (rdx, rptr->radix);
 if ((rptr->flags & REG_VMAD) && sim_vm_fprint_addr)
     sim_vm_fprint_addr (ofile, sim_dflt_dev, (t_addr) val);
-else if (!(rptr->flags & REG_VMIO) ||
-    (fprint_sym (ofile, rdx, &val, NULL, sim_switches | SIM_SW_REG) > 0)) {
+else if (!(rptr->flags & REG_VMFLAGS) ||
+    (fprint_sym (ofile, (rptr->flags & REG_UFMASK) | rdx, &val,
+                 NULL, sim_switches | SIM_SW_REG) > 0)) {
         fprint_val (ofile, val, rdx, rptr->width, rptr->flags & REG_FMT);
         if (rptr->fields) {
             Fprintf (ofile, "\t");
@@ -6603,8 +6604,10 @@ if ((rptr->flags & REG_VMAD) && sim_vm_parse_addr) {    /* address form? */
     if ((tptr == cptr) || (*tptr != 0) || (val > mask))
         return SCPE_ARG;
     }
-else if (!(rptr->flags & REG_VMIO) ||                   /* dont use sym? */
-    (parse_sym (cptr, rdx, NULL, &val, sim_switches | SIM_SW_REG) > SCPE_OK)) {
+else
+    if (!(rptr->flags & REG_VMFLAGS) ||                 /* dont use sym? */
+        (parse_sym (cptr, (rptr->flags & REG_UFMASK) | rdx, NULL,
+                    &val, sim_switches | SIM_SW_REG) > SCPE_OK)) {
     val = get_uint (cptr, rdx, mask, &r);
     if (r != SCPE_OK)
         return SCPE_ARG;
diff --git a/sim_defs.h b/sim_defs.h
index 4e5e28f0..b98ae56c 100644
--- a/sim_defs.h
+++ b/sim_defs.h
@@ -565,6 +565,8 @@ struct sim_reg {
     uint32              qptr;                           /* circ q ptr */
     };
 
+/* Register flags */
+
 #define REG_FMT         00003                           /* see PV_x */
 #define REG_RO          00004                           /* read only */
 #define REG_HIDDEN      00010                           /* hidden */
@@ -576,6 +578,10 @@ struct sim_reg {
 #define REG_FIT         01000                           /* fit access to size */
 #define REG_HRO         (REG_RO | REG_HIDDEN)           /* hidden, read only */
 
+#define REG_V_UF        16                              /* device specific */
+#define REG_UFMASK      (~((1u << REG_V_UF) - 1))       /* user flags mask */
+#define REG_VMFLAGS     (REG_VMIO | REG_UFMASK)         /* call VM routine if any of these are set */
+
 /* Command tables, base and alternate formats */
 
 struct sim_ctab {