diff --git a/src/cpu.c b/src/cpu.c
index 1b9ebec..24ff8f1 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -18,6 +18,8 @@ cpu * new_cpu() {
     m->l = new_lcd();
     m->k = new_keys();
     m->cycle = 0;
+    m->run_to_nop = false;
+    m->run_to_ret = 0;
     return m;
 }
 
@@ -26,4 +28,4 @@ void destroy_cpu(cpu* m) {
   destroy_lcd(m->l);
   destroy_keys(m->k);
   free(m);
-}
\ No newline at end of file
+}
diff --git a/src/cpu.h b/src/cpu.h
index 616e898..797ea12 100644
--- a/src/cpu.h
+++ b/src/cpu.h
@@ -24,9 +24,10 @@
 #define EMU_FLAG_WAIT_FOR_INTERRUPT 0x02
 
 #define CLOCK_SPRINT 0x00
-#define CLOCK_FAST   0x01
-#define CLOCK_SLOW   0x02
-#define CLOCK_STEP   0x04
+#define CLOCK_TURBO  0x01
+#define CLOCK_FAST   0x02
+#define CLOCK_SLOW   0x04
+#define CLOCK_STEP   0x08
 
 typedef struct {
     // clock mode
@@ -65,6 +66,12 @@ typedef struct {
     lcd* l;
     // keys
     keys* k;
+    // whether we should switch to clock mode STEP when the next NOP is encountered
+    bool run_to_nop;
+    // if >0, will be incremented/decremented when encountering JSR/RTS respectively and we'll switch to
+    // STEP when it's decremented to zero, allowing "run until return"
+    int run_to_ret;
+
 } cpu;
 
 cpu * new_cpu();
diff --git a/src/gui.c b/src/gui.c
index b20e91c..2501f51 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -170,6 +170,21 @@ void update_gui(cpu *m) {
 
     // start by populating the monitor
     mvwprintw(wnd_monitor_content, 0, 0, "PC: %04x, OP: %02x (%s)", m->pc_actual, m->opcode, translate_opcode(m->opcode));
+    if (m->run_to_nop && m->opcode == 0xea) {
+      // 0xea is NOP - we use this as a breakpoint
+      m->clock_mode = CLOCK_STEP;
+      m->run_to_nop = false;
+    } else if (m->run_to_ret && m->opcode == 0x60) {
+      // 0x60 is RTS
+      m->run_to_ret--;
+      if (!m->run_to_ret) {
+        // We're returning from the frame where run-to-ret was requested
+        m->clock_mode = CLOCK_STEP;
+      }
+    } else if (m->run_to_ret && m->opcode == 0x20) {
+      // 0x20 is JSR. We want to see an additional return after this, then.
+      m->run_to_ret++;
+    }
     mvwprintw(wnd_monitor_content, 1, 0, "ACC: %02x, X: %02x, Y: %02x, SP: %02x", m->ac, m->x, m->y, m->sp);
     mvwprintw(wnd_monitor_content, 2, 0, "SR: %c%c-%c%c%c%c%c, cycle: %08x",
       m->sr & 0x80 ? 'N' : '-',
@@ -180,7 +195,17 @@ void update_gui(cpu *m) {
       m->sr & 0x02 ? 'Z' : '-',
       m->sr & 0x01 ? 'C' : '-',
       m->cycle);
-    mvwprintw(wnd_monitor_content, 3, 0, "Clock mode: %s", m->clock_mode == CLOCK_FAST ? "FAST" : m->clock_mode == CLOCK_SLOW ? "SLOW" : "STEP");
+    mvwprintw(wnd_monitor_content, 3, 0, "Clock mode: %s", m->clock_mode == CLOCK_TURBO ? "TURBO" : m->clock_mode == CLOCK_FAST ? "FAST " : m->clock_mode == CLOCK_SLOW ? "SLOW " : "STEP ");
+    if (m->run_to_nop) {
+      mvwprintw(wnd_monitor_content, 3, 18, "RTN");
+    } else {
+      mvwprintw(wnd_monitor_content, 3, 18, "   ");
+    }
+    if (m->run_to_ret) {
+      mvwprintw(wnd_monitor_content, 3, 22, "RTR %d", m->run_to_ret);
+    } else {
+      mvwprintw(wnd_monitor_content, 3, 22, "      ");
+    }
     wrefresh(wnd_monitor_content);
 
     // populate memory monitor
@@ -224,6 +249,11 @@ void update_gui(cpu *m) {
 
       switch (m->clock_mode) {
         case CLOCK_SPRINT:
+        case CLOCK_TURBO:
+          cbreak();
+          read = getch();
+          keep_going = true;
+          break;
         case CLOCK_FAST:
           halfdelay(1);
           read = getch();
@@ -260,6 +290,11 @@ void update_gui(cpu *m) {
             m->clock_mode = CLOCK_FAST;
           }
           break;
+        case KEY_F(9): // F9
+          if (!(m->clock_mode == CLOCK_SPRINT)) {
+            m->clock_mode = CLOCK_TURBO;
+          }
+          break;
         case 10:
           m->k->key_enter = true;
           keep_going = true;
@@ -304,7 +339,19 @@ void update_gui(cpu *m) {
             memory_start = 0xfe;
           }
           break;
+        case 'n':
+          if (!(m->clock_mode == CLOCK_SPRINT)) {
+            m->clock_mode = CLOCK_TURBO;
+            m->run_to_nop = true;
+          }
+          break;
+        case 'r':
+          if (!(m->clock_mode == CLOCK_SPRINT)) {
+            m->clock_mode = CLOCK_TURBO;
+            m->run_to_ret = 1;
+          }
+          break;
       } 
     }
   } while (!keep_going && m->clock_mode != CLOCK_SPRINT);
-}
\ No newline at end of file
+}
diff --git a/src/lcd.c b/src/lcd.c
index cb15637..a7f9089 100644
--- a/src/lcd.c
+++ b/src/lcd.c
@@ -33,6 +33,11 @@ void process_input(lcd* l, bool enable, bool rwb, bool data, uint8_t input)
   if (enable && !l->enable_latch) { // rising edge on enable
     l->enable_latch = true;
     trace_emu("LCD rising edge on enable\n");
+    if (rwb && !data) {
+      // There's no command to check - this is read busy flag
+      trace_emu("LCD read busy\n");
+      process_command(l, rwb, l->data);
+    }
     if (!l->initialized && !(input & 0xc0) && (input & CMD_FUNCTION_SET) && !rwb) {
       trace_emu("LCD initializing \n");
       l->initialized = true;
diff --git a/src/opcode_handlers/logical.h b/src/opcode_handlers/logical.h
index 5747f38..c52007d 100644
--- a/src/opcode_handlers/logical.h
+++ b/src/opcode_handlers/logical.h
@@ -167,6 +167,13 @@ case BIT_ZP:
     set_flag(m, FLAG_NEGATIVE, t1 & 0x80);
     break;
 
+case BIT_ZPX:
+    t1 = read_byte(m, ZP(NEXT_BYTE(m) + m->x)); //m->mem[ZP(NEXT_BYTE(m) + m->x)];
+    set_flag(m, FLAG_ZERO, !(t1 & m->ac));
+    set_flag(m, FLAG_OVERFLOW, t1 & 0x40);
+    set_flag(m, FLAG_NEGATIVE, t1 & 0x80);
+    break;
+
 case RMB0:
     r1 = ZP(NEXT_BYTE(m));
     //m->mem[r1] &= ~0x01;
diff --git a/src/opcode_handlers/store.h b/src/opcode_handlers/store.h
index a6aa83e..31f5ea0 100644
--- a/src/opcode_handlers/store.h
+++ b/src/opcode_handlers/store.h
@@ -54,7 +54,7 @@ case STA_INZP:
 
 case STX_ZP:
     r1 = ZP(NEXT_BYTE(m));
-    write_byte(m, r1, m->ac); //m->mem[r1] = m->x;
+    write_byte(m, r1, m->x); //m->mem[r1] = m->x;
     mark_dirty(m, r1);
     break;
 
diff --git a/src/opcodes.h b/src/opcodes.h
index 537abd8..fae72d1 100644
--- a/src/opcodes.h
+++ b/src/opcodes.h
@@ -65,6 +65,7 @@
 
 #define BIT_AB   0x2C
 #define BIT_ZP   0x24
+#define BIT_ZPX  0x34
 
 #define BMI_REL  0x30
 #define BNE_REL  0xD0