diff --git a/src/devices/cpu/hphybrid/hphybrid.cpp b/src/devices/cpu/hphybrid/hphybrid.cpp
index 12258806460..cd45ab81ee5 100644
--- a/src/devices/cpu/hphybrid/hphybrid.cpp
+++ b/src/devices/cpu/hphybrid/hphybrid.cpp
@@ -111,6 +111,7 @@ WRITE_LINE_MEMBER(hp_hybrid_cpu_device::flag_w)
 
 hp_hybrid_cpu_device::hp_hybrid_cpu_device(const machine_config &mconfig, device_type type, const char *name, const char *tag, device_t *owner, UINT32 clock, const char *shortname , UINT8 addrwidth)
         : cpu_device(mconfig, type, name, tag, owner, clock, shortname, __FILE__),
+          m_pa_changed_func(*this),
           m_program_config("program", ENDIANNESS_BIG, 16, addrwidth, -1),
           m_io_config("io", ENDIANNESS_BIG, 16, 6, -1)
 {
@@ -178,6 +179,8 @@ void hp_hybrid_cpu_device::device_start()
                                 save_item(NAME(m_forced_bsc_25));
 
 				m_icountptr = &m_icount;
+
+                                m_pa_changed_func.resolve_safe();
 }
 
 void hp_hybrid_cpu_device::device_reset()
@@ -503,9 +506,11 @@ UINT16 hp_hybrid_cpu_device::execute_one_sub(UINT16 opcode)
 																												if (BIT(m_flags , HPHYBRID_IRH_SVC_BIT)) {
 																																BIT_CLR(m_flags , HPHYBRID_IRH_SVC_BIT);
 																																memmove(&m_reg_PA[ 0 ] , &m_reg_PA[ 1 ] , HPHYBRID_INT_LVLS);
+                                                                                                                                                                                                                                                                m_pa_changed_func((UINT8)CURRENT_PA);
 																												} else if (BIT(m_flags , HPHYBRID_IRL_SVC_BIT)) {
 																																BIT_CLR(m_flags , HPHYBRID_IRL_SVC_BIT);
 																																memmove(&m_reg_PA[ 0 ] , &m_reg_PA[ 1 ] , HPHYBRID_INT_LVLS);
+                                                                                                                                                                                                                                                                m_pa_changed_func((UINT8)CURRENT_PA);
 																												}
 																								}
 																								tmp = RM(AEC_CASE_C , m_reg_R--) + (opcode & 0x1f);
@@ -755,6 +760,7 @@ void hp_hybrid_cpu_device::WM(UINT32 addr , UINT16 v)
 
                 case HP_REG_PA_ADDR:
                         CURRENT_PA = v & HP_REG_PA_MASK;
+                        m_pa_changed_func((UINT8)CURRENT_PA);
                         break;
 
                 case HP_REG_W_ADDR:
@@ -1007,6 +1013,8 @@ void hp_hybrid_cpu_device::check_for_interrupts(void)
 
 				CURRENT_PA = new_PA;
 
+                                m_pa_changed_func((UINT8)CURRENT_PA);
+
 				// Is this correct? Patent @ pg 210 suggests that the whole interrupt recognition sequence
 				// lasts for 32 cycles (6 are already accounted for in get_ea for one indirection)
 				m_icount -= 26;
@@ -1456,7 +1464,7 @@ UINT32 hp_5061_3001_cpu_device::add_mae(aec_cases_t aec_case , UINT16 addr)
         bool top_half = BIT(addr , 15) != 0;
 
         // Detect accesses to top half of base page
-        if ((addr & 0xfe00) == 0xfe00) {
+        if (aec_case == AEC_CASE_C && (addr & 0xfe00) == 0xfe00) {
             aec_case = AEC_CASE_B;
         }
 
diff --git a/src/devices/cpu/hphybrid/hphybrid.h b/src/devices/cpu/hphybrid/hphybrid.h
index 33124ab19ee..2b59a44120b 100644
--- a/src/devices/cpu/hphybrid/hphybrid.h
+++ b/src/devices/cpu/hphybrid/hphybrid.h
@@ -16,6 +16,7 @@
 //   and "enabling" resource of all
 // - US Patent 4,180,854 describing the HP9845 system
 // - Study of disassembly of firmware of HP64000 & HP9845 systems
+// - hp9800e emulator for inspiration on implementing EMC instructions
 // - A lot of "educated" guessing
 
 #ifndef _HPHYBRID_H_
@@ -74,6 +75,10 @@
 #define MCFG_HPHYBRID_SET_9845_BOOT(_mode) \
 	hp_5061_3001_cpu_device::set_boot_mode_static(*device, _mode);
 
+// PA changed callback
+#define MCFG_HPHYBRID_PA_CHANGED(_devcb) \
+        hp_hybrid_cpu_device::set_pa_changed_func(*device , DEVCB_##_devcb);
+
 class hp_hybrid_cpu_device : public cpu_device
 {
 public:
@@ -82,6 +87,8 @@ public:
                 DECLARE_WRITE_LINE_MEMBER(status_w);
                 DECLARE_WRITE_LINE_MEMBER(flag_w);
 
+        template<class _Object> static devcb_base &set_pa_changed_func(device_t &device, _Object object) { return downcast<hp_hybrid_cpu_device &>(device).m_pa_changed_func.set_callback(object); }
+
 protected:
         hp_hybrid_cpu_device(const machine_config &mconfig, device_type type, const char *name, const char *tag, device_t *owner, UINT32 clock, const char *shortname , UINT8 addrwidth);
 
@@ -138,6 +145,8 @@ protected:
         
         UINT16 get_skip_addr(UINT16 opcode , bool condition) const;
 
+        devcb_write8 m_pa_changed_func;
+
                 int m_icount;
         bool m_forced_bsc_25;