diff --git a/src/devices/cpu/mcs96/i8x9x.cpp b/src/devices/cpu/mcs96/i8x9x.cpp
index 0c986bdcd23..792cc1378bb 100644
--- a/src/devices/cpu/mcs96/i8x9x.cpp
+++ b/src/devices/cpu/mcs96/i8x9x.cpp
@@ -20,18 +20,16 @@ i8x9x_device::i8x9x_device(const machine_config &mconfig, device_type type, cons
 	m_in_p0_cb(*this),
 	m_out_p1_cb(*this), m_in_p1_cb(*this),
 	m_out_p2_cb(*this), m_in_p2_cb(*this),
-	base_timer2(0), ad_done(0), hsi_mode(0), hsi_status(0), hso_command(0), ad_command(0), hso_time(0), ad_result(0), pwm_control(0),
+	base_timer2(0), ad_done(0), hsi_mode(0), hsi_status(0), hso_command(0), ad_command(0), hso_active(0), hso_time(0), ad_result(0), pwm_control(0),
 	port1(0), port2(0),
 	ios0(0), ios1(0), ioc0(0), ioc1(0), extint(false),
 	sbuf(0), sp_con(0), sp_stat(0), serial_send_buf(0), serial_send_timer(0), baud_reg(0), brh(false)
 {
 	for (auto &hso : hso_info)
 	{
-		hso.active = false;
 		hso.command = 0;
 		hso.time = 0;
 	}
-	hso_cam_hold.active = false;
 	hso_cam_hold.command = 0;
 	hso_cam_hold.time = 0;
 }
@@ -77,16 +75,11 @@ void i8x9x_device::device_start()
 	state_add<u8>(I8X9X_PORT2,   "PORT2",       [this]() -> u8 { return port2; }, [this](u8 data) { port2_w(data); }).mask(i8x9x_p2_mask());
 	state_add(I8X9X_IOC0,        "IOC0",        ioc0).mask(0xfd);
 	state_add(I8X9X_IOC1,        "IOC1",        ioc1);
-	state_add(I8X9X_IOS0,        "IOS0",        ios0);
+	state_add<u8>(I8X9X_IOS0,    "IOS0",        [this]() -> u8 { return ios0; }, [this](u8 data) { ios0_w(data); });
 	state_add(I8X9X_IOS1,        "IOS1",        ios1);
 
-	for(int i = 0; i < 8; i++)
-	{
-		save_item(NAME(hso_info[i].active), i);
-		save_item(NAME(hso_info[i].command), i);
-		save_item(NAME(hso_info[i].time), i);
-	}
-	save_item(NAME(hso_cam_hold.active));
+	save_item(STRUCT_MEMBER(hso_info, command));
+	save_item(STRUCT_MEMBER(hso_info, time));
 	save_item(NAME(hso_cam_hold.command));
 	save_item(NAME(hso_cam_hold.time));
 
@@ -96,6 +89,7 @@ void i8x9x_device::device_start()
 	save_item(NAME(hsi_status));
 	save_item(NAME(hso_command));
 	save_item(NAME(ad_command));
+	save_item(NAME(hso_active));
 	save_item(NAME(hso_time));
 	save_item(NAME(ad_result));
 	save_item(NAME(port1));
@@ -118,9 +112,7 @@ void i8x9x_device::device_start()
 void i8x9x_device::device_reset()
 {
 	mcs96_device::device_reset();
-	for (auto &hso : hso_info)
-		hso.active = false;
-	hso_cam_hold.active = false;
+	hso_active = 0;
 	hso_command = 0;
 	hso_time = 0;
 	timer2_reset(total_cycles());
@@ -144,15 +136,17 @@ void i8x9x_device::device_reset()
 void i8x9x_device::commit_hso_cam()
 {
 	for(int i=0; i<8; i++)
-		if(!hso_info[i].active) {
+		if(!BIT(hso_active, i)) {
 			//logerror("hso cam %02x %04x in slot %d (%04x)\n", hso_command, hso_time, i, PPC);
-			hso_info[i].active = true;
+			hso_active |= 1 << i;
+			if(hso_active == 0xff)
+				ios0 |= 0x40;
 			hso_info[i].command = hso_command;
 			hso_info[i].time = hso_time;
 			internal_update(total_cycles());
 			return;
 		}
-	hso_cam_hold.active = true;
+	ios0 |= 0xc0;
 	hso_cam_hold.command = hso_command;
 	hso_cam_hold.time = hso_time;
 }
@@ -271,7 +265,7 @@ void i8x9x_device::watchdog_w(u8 data)
 u16 i8x9x_device::timer1_r()
 {
 	u16 data = timer_value(1, total_cycles());
-	if (!machine().side_effects_disabled())
+	if (0 && !machine().side_effects_disabled())
 		logerror("read timer1 %04x (%04x)\n", data, PPC);
 	return data;
 }
@@ -366,6 +360,14 @@ u8 i8x9x_device::ios0_r()
 	return ios0;
 }
 
+void i8x9x_device::ios0_w(u8 data)
+{
+	u8 mask = (data ^ ios0) & 0x3f;
+	ios0 = (data & 0x3f) | (ios0 & 0xc0);
+	if (mask != 0)
+		m_hso_cb(0, data & 0x3f, mask);
+}
+
 void i8x9x_device::ioc1_w(u8 data)
 {
 	ioc1 = data;
@@ -438,7 +440,9 @@ void i8x9x_device::set_hsi_state(int pin, bool state)
 void i8x9x_device::trigger_cam(int id, u64 current_time)
 {
 	hso_cam_entry &cam = hso_info[id];
-	cam.active = false;
+	if(hso_active == 0xff && !BIT(ios0, 7))
+		ios0 &= 0xbf;
+	hso_active &= ~(1 << id);
 	switch(cam.command & 0x0f) {
 	case 0x0: case 0x1: case 0x2: case 0x3: case 0x4: case 0x5:
 		set_hso(1 << (cam.command & 7), BIT(cam.command, 5));
@@ -491,7 +495,7 @@ void i8x9x_device::internal_update(u64 current_time)
 	u16 current_timer2 = timer_value(2, current_time);
 
 	for(int i=0; i<8; i++)
-		if(hso_info[i].active) {
+		if(BIT(hso_active, i)) {
 			u8 cmd = hso_info[i].command;
 			u16 t = hso_info[i].time;
 			if(((cmd & 0x40) && t == current_timer2) ||
@@ -514,12 +518,15 @@ void i8x9x_device::internal_update(u64 current_time)
 
 	u64 event_time = 0;
 	for(int i=0; i<8; i++) {
-		if(!hso_info[i].active && hso_cam_hold.active) {
+		if(!BIT(hso_active, i) && BIT(ios0, 7)) {
 			hso_info[i] = hso_cam_hold;
-			hso_cam_hold.active = false;
-			logerror("%s: hso cam %02x %04x in slot %d from hold\n", tag(), hso_cam_hold.command, hso_cam_hold.time, i);
+			hso_active |= 1 << i;
+			ios0 &= 0x7f;
+			if(hso_active == 0xff)
+				ios0 |= 0x40;
+			logerror("hso cam %02x %04x in slot %d from hold\n", hso_cam_hold.command, hso_cam_hold.time, i);
 		}
-		if(hso_info[i].active) {
+		if(BIT(hso_active, i)) {
 			u64 new_time = timer_time_until(hso_info[i].command & 0x40 ? 2 : 1, current_time, hso_info[i].time);
 			if(!event_time || new_time < event_time)
 				event_time = new_time;
diff --git a/src/devices/cpu/mcs96/i8x9x.h b/src/devices/cpu/mcs96/i8x9x.h
index bb0cc710b24..5f4ab03f8a5 100644
--- a/src/devices/cpu/mcs96/i8x9x.h
+++ b/src/devices/cpu/mcs96/i8x9x.h
@@ -106,6 +106,7 @@ protected:
 	u8 sp_stat_r();
 	void ioc0_w(u8 data);
 	u8 ios0_r();
+	void ios0_w(u8 data);
 	void ioc1_w(u8 data);
 	u8 ios1_r();
 	void pwm_control_w(u8 data);
@@ -123,7 +124,6 @@ private:
 	};
 
 	struct hso_cam_entry {
-		bool active;
 		u8 command;
 		u16 time;
 	};
@@ -144,7 +144,7 @@ private:
 	hso_cam_entry hso_cam_hold;
 
 	u64 base_timer2, ad_done;
-	u8 hsi_mode, hsi_status, hso_command, ad_command;
+	u8 hsi_mode, hsi_status, hso_command, ad_command, hso_active;
 	u16 hso_time, ad_result;
 	u8 pwm_control;
 	u8 port1, port2;