diff --git a/tgt-vvp/vvp_process.c b/tgt-vvp/vvp_process.c
index cac098fd3..8fa8830dc 100644
--- a/tgt-vvp/vvp_process.c
+++ b/tgt-vvp/vvp_process.c
@@ -802,7 +802,7 @@ static void force_vector_to_lval(ivl_statement_t net, struct vector_info rvec)
       switch (ivl_statement_type(net)) {
 	  case IVL_ST_CASSIGN:
 	    command_name = "%cassign/v";
-	    command_name_x0 = "ERROR";
+	    command_name_x0 = "%cassign/x0";
 	    break;
 	  case IVL_ST_FORCE:
 	    command_name = "%force/v";
@@ -842,12 +842,6 @@ static void force_vector_to_lval(ivl_statement_t net, struct vector_info rvec)
 
 	    if (part_off != 0 || use_wid != ivl_signal_width(lsig)) {
 
-		  if (ivl_statement_type(net) == IVL_ST_CASSIGN) {
-			fprintf(stderr, "%s:%u: vvp-tgt sorry: cannot assign "
-			        "signal to a bit/part select.\n",
-			        ivl_stmt_file(net), ivl_stmt_lineno(net));
-			exit(1);
-		  }
 		  command_name = command_name_x0;
 		  fprintf(vvp_out, "    %%ix/load 0, %u;\n", part_off);
 
@@ -967,15 +961,12 @@ static int show_stmt_deassign(ivl_statement_t net)
 	    assert(lsig != 0);
 	    assert(ivl_lval_mux(lval) == 0);
 
-	      /* We do not currently support deassigning a bit or
-	       * part select. */
+	    unsigned use_wid = ivl_lval_width(lval);
 	    ivl_expr_t part_off_ex = ivl_lval_part_off(lval);
-	    if (ivl_signal_width(lsig) > ivl_lval_width(lval) ||
-	        (part_off_ex && get_number_immediate(part_off_ex) != 0)) {
-		  fprintf(stderr, "%s:%u: vvp-tgt sorry: cannot deassign "
-		  "a bit/part select.\n", ivl_stmt_file(net),
-		  ivl_stmt_lineno(net));
-		  exit(1);
+	    unsigned part_off = 0;
+	    if (part_off_ex != 0) {
+		  assert(number_is_immediate(part_off_ex, 64));
+		  part_off = get_number_immediate(part_off_ex);
 	    }
 
 	    if (word_idx != 0) {
@@ -984,7 +975,8 @@ static int show_stmt_deassign(ivl_statement_t net)
 	    }
 
 
-	    fprintf(vvp_out, "    %%deassign v%p_%lu;\n", lsig, use_word);
+	    fprintf(vvp_out, "    %%deassign v%p_%lu, %u, %u;\n",
+		    lsig, use_word, part_off, use_wid);
       }
 
       return 0;
diff --git a/vvp/codes.h b/vvp/codes.h
index 0b0f7dad7..6cb5c3852 100644
--- a/vvp/codes.h
+++ b/vvp/codes.h
@@ -52,6 +52,7 @@ extern bool of_BLEND_WR(vthread_t thr, vvp_code_t code);
 extern bool of_BREAKPOINT(vthread_t thr, vvp_code_t code);
 extern bool of_CASSIGN_LINK(vthread_t thr, vvp_code_t code);
 extern bool of_CASSIGN_V(vthread_t thr, vvp_code_t code);
+extern bool of_CASSIGN_X0(vthread_t thr, vvp_code_t code);
 extern bool of_CMPIS(vthread_t thr, vvp_code_t code);
 extern bool of_CMPIU(vthread_t thr, vvp_code_t code);
 extern bool of_CMPS(vthread_t thr, vvp_code_t code);
diff --git a/vvp/compile.cc b/vvp/compile.cc
index ff073ab2f..608232b95 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -101,6 +101,7 @@ const static struct opcode_table_s opcode_table[] = {
       { "%breakpoint", of_BREAKPOINT, 0,  {OA_NONE, OA_NONE, OA_NONE} },
       { "%cassign/link",of_CASSIGN_LINK,2,{OA_FUNC_PTR,OA_FUNC_PTR2,OA_NONE} },
       { "%cassign/v",of_CASSIGN_V,3,{OA_FUNC_PTR,OA_BIT1,    OA_BIT2} },
+      { "%cassign/x0",of_CASSIGN_X0,3,{OA_FUNC_PTR,OA_BIT1,  OA_BIT2} },
       { "%cmp/s",  of_CMPS,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%cmp/u",  of_CMPU,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%cmp/wr", of_CMPWR,  2,  {OA_BIT1,     OA_BIT2,     OA_NONE} },
@@ -113,7 +114,7 @@ const static struct opcode_table_s opcode_table[] = {
       { "%cvt/ir", of_CVT_IR, 2,  {OA_BIT1,     OA_BIT2,     OA_NONE} },
       { "%cvt/ri", of_CVT_RI, 2,  {OA_BIT1,     OA_BIT2,     OA_NONE} },
       { "%cvt/vr", of_CVT_VR, 3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
-      { "%deassign",of_DEASSIGN,1,{OA_FUNC_PTR, OA_NONE,     OA_NONE} },
+      { "%deassign",of_DEASSIGN,3,{OA_FUNC_PTR, OA_BIT1,     OA_BIT2} },
       { "%delay",  of_DELAY,  2,  {OA_BIT1,     OA_BIT2,     OA_NONE} },
       { "%delayx", of_DELAYX, 1,  {OA_NUMBER,   OA_NONE,     OA_NONE} },
       { "%div",    of_DIV,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
diff --git a/vvp/opcodes.txt b/vvp/opcodes.txt
index 05156a6ae..6d7c6afa7 100644
--- a/vvp/opcodes.txt
+++ b/vvp/opcodes.txt
@@ -168,6 +168,13 @@ variable. This is similar to %set, but it uses the cassign port
 signal responds differently. See "VARIABLE STATEMENTS" in the
 README.txt file.
 
+* %cassign/x0 <label>, <bit>, <wid>
+
+Perform continuous assign of a constant value to part of the target
+variable. This is similar to %set/x instruction, but it uses the
+cassign port (port-1) of the signal functor instead of the normal
+assign port (port-0), so the signal responds differently. See
+"VARIABLE STATEMENTS" and "NET STATEMENTS" in the README.txt file.
 
 * %cmp/u <bit-l>, <bit-r>, <wid>
 * %cmp/s <bit-l>, <bit-r>, <wid>
@@ -239,11 +246,15 @@ The %cvt/vr opcode converts a real word <bit-r> to a thread vector
 starting at <bit-l> and with the width <wid>. Non-integer precision is
 lost in the conversion.
 
-* %deassign <var-label>
+* %deassign <var-label>, <base>, <width>
 
 Deactivate and disconnect a procedural continuous assignment to a
 variable. The <var-label> identifies the affected variable.
 
+The <base> and <width> are used to determine what part of the signal
+will be deactivated. For a full deactivation the <base> is 0 and
+<width> is the entire signal width.
+
 * %delay <delay>
 
 This opcode pauses the thread, and causes it to be rescheduled for a
@@ -291,8 +302,8 @@ in the README.txt file.
 
 * %force/x0 <label>, <bit>, <wid>
 
-Force a constant value to part target variable. This is similar to
-%set/x instruction, but it uses the force port (port-2) of the signal
+Force a constant value to part of the target variable. This is similar
+to %set/x instruction, but it uses the force port (port-2) of the signal
 functor instead of the normal assign port (port-0), so the signal
 responds differently. See "VARIABLE STATEMENTS" and "NET STATEMENTS"
 in the README.txt file.
diff --git a/vvp/vthread.cc b/vvp/vthread.cc
index b59d94979..d97fdf48b 100644
--- a/vvp/vthread.cc
+++ b/vvp/vthread.cc
@@ -845,6 +845,40 @@ bool of_CASSIGN_V(vthread_t thr, vvp_code_t cp)
       return true;
 }
 
+bool of_CASSIGN_X0(vthread_t thr, vvp_code_t cp)
+{
+      vvp_net_t*net = cp->net;
+      unsigned base = cp->bit_idx[0];
+      unsigned wid = cp->bit_idx[1];
+
+	// Implicitly, we get the base into the target vector from the
+	// X0 register.
+      long index = thr->words[0].w_int;
+
+      vvp_fun_signal_vec*sig = dynamic_cast<vvp_fun_signal_vec*> (net->fun);
+
+      if (index < 0 && (wid <= (unsigned)-index))
+	    return true;
+
+      if (index >= (long)sig->size())
+	    return true;
+
+      if (index < 0) {
+	    wid -= (unsigned) -index;
+	    index = 0;
+      }
+
+      if (index+wid > sig->size())
+	    wid = sig->size() - index;
+
+      vvp_vector4_t vector = vthread_bits_to_vector(thr, base, wid);
+
+      vvp_net_ptr_t ptr (net, 1);
+      vvp_send_vec4_pv(ptr, vector, index, wid, sig->size());
+
+      return true;
+}
+
 bool of_CMPS(vthread_t thr, vvp_code_t cp)
 {
       vvp_bit4_t eq  = BIT4_1;
@@ -1185,9 +1219,24 @@ bool of_CVT_VR(vthread_t thr, vvp_code_t cp)
 bool of_DEASSIGN(vthread_t thr, vvp_code_t cp)
 {
       vvp_net_t*net = cp->net;
+      unsigned base  = cp->bit_idx[0];
+      unsigned width = cp->bit_idx[1];
 
+      vvp_fun_signal_vec*sig = reinterpret_cast<vvp_fun_signal_vec*>(net->fun);
+      assert(sig);
+
+      if (base >= sig->size()) return true;
+      if (base+width > sig->size()) width = sig->size() - base;
+
+      bool full_sig = base == 0 && width == sig->size();
+
+	/* Do we release all or part of the net? */
       vvp_net_ptr_t ptr (net, 3);
-      vvp_send_long(ptr, 1);
+      if (full_sig) {
+	    vvp_send_long(ptr, 1);
+      } else {
+	    vvp_send_long_pv(ptr, 1, base, width);
+      }
 
       return true;
 }
@@ -1777,7 +1826,7 @@ bool of_FORCE_V(vthread_t thr, vvp_code_t cp)
 	/* Collect the thread bits into a vector4 item. */
       vvp_vector4_t value = vthread_bits_to_vector(thr, base, wid);
 
-	/* set the value into port 1 of the destination. */
+	/* Set the value into port 2 of the destination. */
       vvp_net_ptr_t ptr (net, 2);
       vvp_send_vec4(ptr, value);
 
@@ -1787,7 +1836,7 @@ bool of_FORCE_V(vthread_t thr, vvp_code_t cp)
 bool of_FORCE_X0(vthread_t thr, vvp_code_t cp)
 {
       vvp_net_t*net = cp->net;
-      unsigned bit = cp->bit_idx[0];
+      unsigned base = cp->bit_idx[0];
       unsigned wid = cp->bit_idx[1];
 
 	// Implicitly, we get the base into the target vector from the
@@ -1810,19 +1859,14 @@ bool of_FORCE_X0(vthread_t thr, vvp_code_t cp)
       if (index+wid > sig->size())
 	    wid = sig->size() - index;
 
-      vvp_vector4_t bit_vec(wid);
-      for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
-	    vvp_bit4_t bit_val = thr_get_bit(thr, bit);
-	    bit_vec.set_bit(idx, bit_val);
-	    if (bit >= 4)
-		  bit += 1;
-      }
+      vvp_vector4_t vector = vthread_bits_to_vector(thr, base, wid);
 
       vvp_net_ptr_t ptr (net, 2);
-      vvp_send_vec4_pv(ptr, bit_vec, index, wid, sig->size());
+      vvp_send_vec4_pv(ptr, vector, index, wid, sig->size());
 
       return true;
 }
+
 /*
  * The %fork instruction causes a new child to be created and pushed
  * in front of any existing child. This causes the new child to be the
diff --git a/vvp/vvp_net.cc b/vvp/vvp_net.cc
index 638bcdbe5..3697e6c12 100644
--- a/vvp/vvp_net.cc
+++ b/vvp/vvp_net.cc
@@ -1133,6 +1133,18 @@ bool vvp_vector2_t::is_NaN() const
       return wid_ == 0;
 }
 
+bool vvp_vector2_t::is_zero() const
+{
+      const unsigned words = (wid_ + BITS_PER_WORD-1) / BITS_PER_WORD;
+
+      for (unsigned idx = 0; idx < words; idx += 1) {
+	    if (vec_[idx] == 0) continue;
+	    return false;
+      }
+
+      return true;
+}
+
 /*
  * Basic idea from "Introduction to Programming using SML" by
  * Michael R. Hansen and Hans Rischel page 261 and "Seminumerical
@@ -1659,6 +1671,18 @@ vvp_fun_signal_base::vvp_fun_signal_base()
 void vvp_fun_signal_base::deassign()
 {
       continuous_assign_active_ = false;
+      assign_mask_ = vvp_vector2_t();
+}
+
+void vvp_fun_signal_base::deassign_pv(unsigned base, unsigned wid)
+{
+      for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+	    assign_mask_.set_bit(base+idx, 0);
+      }
+
+      if (assign_mask_.is_zero()) {
+	    assign_mask_ = vvp_vector2_t();
+      }
 }
 
 /*
@@ -1700,9 +1724,7 @@ void vvp_fun_signal_base::recv_long_pv(vvp_net_ptr_t ptr, long bit,
 	  case 3: // Command port
 	    switch (bit) {
 		case 1: // deassign command
-		  fprintf(stderr, "Sorry: cannot deassign a partial signal\n");
-		  assert(0);
-		  deassign();
+		  deassign_pv(base, wid);
 		  break;
 		case 2: // release/net
 		  release_pv(ptr, true, base, wid);
@@ -1745,22 +1767,34 @@ void vvp_fun_signal::recv_vec4(vvp_net_ptr_t ptr, const vvp_vector4_t&bit)
 {
       switch (ptr.port()) {
 	  case 0: // Normal input (feed from net, or set from process)
-	      /* If continuous assign is active, then this is a var
-		 and the continuous assigned values overrides any
-		 normal input. So process input only if continuous
-		 assignment is not active. */
-	    if (!continuous_assign_active_) {
+	      /* If we don't have a continuous assign mask then just
+		 copy the bits, otherwise we need to see if there are
+		 any holes in the mask so we can set those bits. */
+	    if (assign_mask_.size() == 0) {
 		  if (needs_init_ || !bits4_.eeq(bit)) {
 			bits4_ = bit;
 			needs_init_ = false;
 			calculate_output_(ptr);
 		  }
+	    } else {
+		  bool changed = false;
+		  assert(bits4_.size() == assign_mask_.size());
+		  for (unsigned idx = 0 ;  idx < bit.size() ;  idx += 1) {
+			if (idx >= bits4_.size()) break;
+			if (assign_mask_.value(idx)) continue;
+			bits4_.set_bit(idx, bit.value(idx));
+			changed = true;
+		  }
+		  if (changed) {
+			needs_init_ = false;
+			calculate_output_(ptr);
+		  }
 	    }
 	    break;
 
 	  case 1: // Continuous assign value
-	    continuous_assign_active_ = true;
 	    bits4_ = bit;
+	    assign_mask_ = vvp_vector2_t(vvp_vector2_t::FILL1, size());
 	    calculate_output_(ptr);
 	    break;
 
@@ -1792,17 +1826,41 @@ void vvp_fun_signal::recv_vec4_pv(vvp_net_ptr_t ptr, const vvp_vector4_t&bit,
 
       switch (ptr.port()) {
 	  case 0: // Normal input
-	    if (! continuous_assign_active_) {
+	    if (assign_mask_.size() == 0) {
 		  for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
-			if (base+idx >= bits4_.size())
-			      break;
+			if (base+idx >= bits4_.size()) break;
 			bits4_.set_bit(base+idx, bit.value(idx));
 		  }
 		  needs_init_ = false;
 		  calculate_output_(ptr);
+	    } else {
+		  bool changed = false;
+		  assert(bits4_.size() == assign_mask_.size());
+		  for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+			if (base+idx >= bits4_.size()) break;
+			if (assign_mask_.value(base+idx)) continue;
+			bits4_.set_bit(base+idx, bit.value(idx));
+			changed = true;
+		  }
+		  if (changed) {
+			needs_init_ = false;
+			calculate_output_(ptr);
+		  }
 	    }
 	    break;
 
+	  case 1: // Continuous assign value
+	    if (assign_mask_.size() == 0)
+		  assign_mask_ = vvp_vector2_t(vvp_vector2_t::FILL0, size());
+	    for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+		  if (base+idx >= bits4_.size())
+			break;
+		  bits4_.set_bit(base+idx, bit.value(idx));
+		  assign_mask_.set_bit(base+idx, 1);
+	    }
+	    calculate_output_(ptr);
+	    break;
+
 	  case 2: // Force value
 
 	    if (force_mask_.size() == 0)
@@ -1870,6 +1928,7 @@ void vvp_fun_signal::release_pv(vvp_net_ptr_t ptr, bool net,
 	    force_mask_.set_bit(base+idx, 0);
 	    if (!net) bits4_.set_bit(base+idx, force_.value(base+idx));
       }
+      if (force_mask_.is_zero()) force_mask_ = vvp_vector2_t();
 
       if (net) calculate_output_(ptr);
 }
@@ -1929,19 +1988,18 @@ void vvp_fun_signal8::recv_vec8(vvp_net_ptr_t ptr, vvp_vector8_t bit)
 {
       switch (ptr.port()) {
 	  case 0: // Normal input (feed from net, or set from process)
-	    if (!continuous_assign_active_) {
-		  if (needs_init_ || !bits8_.eeq(bit)) {
-			bits8_ = bit;
-			needs_init_ = false;
-			calculate_output_(ptr);
-		  }
+	    if (needs_init_ || !bits8_.eeq(bit)) {
+		  bits8_ = bit;
+		  needs_init_ = false;
+		  calculate_output_(ptr);
 	    }
 	    break;
 
 	  case 1: // Continuous assign value
-	    continuous_assign_active_ = true;
-	    bits8_ = bit;
-	    calculate_output_(ptr);
+	    /* This is a procedural continuous assign and it can
+	     * only be used on a register and a register is never
+	     * strength aware. */
+	    assert(0);
 	    break;
 
 	  case 2: // Force value
@@ -1964,6 +2022,57 @@ void vvp_fun_signal8::recv_vec8(vvp_net_ptr_t ptr, vvp_vector8_t bit)
       }
 }
 
+void vvp_fun_signal8::recv_vec4_pv(vvp_net_ptr_t ptr, const vvp_vector4_t&bit,
+                                   unsigned base, unsigned wid, unsigned vwid)
+{
+      recv_vec8_pv(ptr, bit, base, wid, vwid);
+}
+
+void vvp_fun_signal8::recv_vec8_pv(vvp_net_ptr_t ptr, vvp_vector8_t bit,
+				   unsigned base, unsigned wid, unsigned vwid)
+{
+      assert(bit.size() == wid);
+      assert(bits8_.size() == vwid);
+
+      switch (ptr.port()) {
+	  case 0: // Normal input
+	    for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+		  if (base+idx >= bits8_.size()) break;
+		  bits8_.set_bit(base+idx, bit.value(idx));
+	    }
+	    needs_init_ = false;
+	    calculate_output_(ptr);
+	    break;
+
+	  case 1: // Continuous assign value
+	    /* This is a procedural continuous assign and it can
+	     * only be used on a register and a register is never
+	     * strength aware. */
+	    assert(0);
+	    break;
+
+	  case 2: // Force value
+
+	    if (force_mask_.size() == 0)
+		  force_mask_ = vvp_vector2_t(vvp_vector2_t::FILL0, size());
+	    if (force_.size() == 0)
+		  force_ = vvp_vector8_t(vvp_vector4_t(vwid, BIT4_Z));
+
+	    for (unsigned idx = 0 ;  idx < wid ;  idx += 1) {
+		  force_mask_.set_bit(base+idx, 1);
+		  force_.set_bit(base+idx, bit.value(idx));
+	    }
+
+	    calculate_output_(ptr);
+	    break;
+
+	  default:
+	    fprintf(stderr, "Unsupported port type %d.\n", ptr.port());
+	    assert(0);
+	    break;
+      }
+}
+
 void vvp_fun_signal8::calculate_output_(vvp_net_ptr_t ptr)
 {
       if (force_mask_.size()) {
@@ -2003,6 +2112,7 @@ void vvp_fun_signal8::release_pv(vvp_net_ptr_t ptr, bool net,
 	    force_mask_.set_bit(base+idx, 0);
 	    if (!net) bits8_.set_bit(base+idx, force_.value(base+idx));
       }
+      if (force_mask_.is_zero()) force_mask_ = vvp_vector2_t();
 
       if (net) calculate_output_(ptr);
 }
@@ -2025,9 +2135,14 @@ vvp_bit4_t vvp_fun_signal8::value(unsigned idx) const
 
 vvp_vector4_t vvp_fun_signal8::vec4_value() const
 {
-      if (force_mask_.size())
-	    return reduce4(force_);
-      else
+      if (force_mask_.size()) {
+	    vvp_vector8_t bits (bits8_);
+	    for (unsigned idx = 0 ;  idx < bits.size() ;  idx += 1) {
+		  if (force_mask_.value(idx))
+			bits.set_bit(idx, force_.value(idx));
+	    }
+	    return reduce4(bits);
+      } else
 	    return reduce4(bits8_);
 }
 
diff --git a/vvp/vvp_net.h b/vvp/vvp_net.h
index b8eee8e4e..6c169a19e 100644
--- a/vvp/vvp_net.h
+++ b/vvp/vvp_net.h
@@ -306,6 +306,7 @@ class vvp_vector2_t {
       vvp_vector2_t&operator = (const vvp_vector2_t&);
 
       bool is_NaN() const;
+      bool is_zero() const;
       unsigned size() const;
       int value(unsigned idx) const;
       void set_bit(unsigned idx, int bit);
@@ -834,8 +835,10 @@ class vvp_fun_signal_base : public vvp_net_fun_t, public vvp_vpi_callback {
       bool needs_init_;
       bool continuous_assign_active_;
       vvp_vector2_t force_mask_;
+      vvp_vector2_t assign_mask_;
 
       void deassign();
+      void deassign_pv(unsigned base, unsigned wid);
       virtual void release(vvp_net_ptr_t ptr, bool net) =0;
       virtual void release_pv(vvp_net_ptr_t ptr, bool net,
                               unsigned base, unsigned wid) =0;
@@ -896,8 +899,10 @@ class vvp_fun_signal8  : public vvp_fun_signal_vec {
       void recv_vec8(vvp_net_ptr_t port, vvp_vector8_t bit);
 
 	// Part select variants of above
-	//void recv_vec4_pv(vvp_net_ptr_t port, const vvp_vector4_t&bit,
-	//			unsigned base, unsigned wid, unsigned vwid);
+      void recv_vec4_pv(vvp_net_ptr_t port, const vvp_vector4_t&bit,
+                        unsigned base, unsigned wid, unsigned vwid);
+      void recv_vec8_pv(vvp_net_ptr_t port, vvp_vector8_t bit,
+                        unsigned base, unsigned wid, unsigned vwid);
 
 	// Get information about the vector value.
       unsigned   size() const;