diff --git a/src/mame/nec/bungo.cpp b/src/mame/nec/bungo.cpp
index 5dc2b7210de..1794725def4 100644
--- a/src/mame/nec/bungo.cpp
+++ b/src/mame/nec/bungo.cpp
@@ -136,6 +136,9 @@ void bungo_mini5sx_state::mini5sx_config(machine_config &config)
 //  m_ppi_sys->in_pc_callback().set_constant(0xa0); // 0x80 cpu triple fault reset flag?
 //  m_ppi_sys->out_pc_callback().set(FUNC(pc98lt_state::ppi_sys_beep_portc_w));
 
+    // TODO: unverified, known to have a serial port
+    pc9801_serial(config);
+
 	I8255(config, m_ppi_prn, 0);
 //  m_ppi_prn->in_pb_callback().set_ioport("PRNB");
 
diff --git a/src/mame/nec/bungo.h b/src/mame/nec/bungo.h
index f0af4b8f2aa..385b9022835 100644
--- a/src/mame/nec/bungo.h
+++ b/src/mame/nec/bungo.h
@@ -38,6 +38,9 @@ private:
 
 	u16 fake_dict_r(offs_t offset);
 
+    // just suppress for now, TBD
+	virtual void uart_irq_check() override {};
+
 	void bungo_palette(palette_device &palette) const;
 	uint32_t screen_update(screen_device &screen, bitmap_rgb32 &bitmap, const rectangle &cliprect);
 };
diff --git a/src/mame/nec/pc9801.cpp b/src/mame/nec/pc9801.cpp
index 03795f9c082..24079224f0d 100644
--- a/src/mame/nec/pc9801.cpp
+++ b/src/mame/nec/pc9801.cpp
@@ -356,6 +356,7 @@ Keyboard TX commands:
 
 #include "emu.h"
 #include "pc9801.h"
+
 #include "machine/input_merger.h"
 
 void pc98_base_state::rtc_w(uint8_t data)
@@ -1657,9 +1658,25 @@ u8 pc9801_state::ppi_sys_portb_r()
 	return res;
 }
 
+void pc9801_state::uart_irq_check()
+{
+	m_pic1->ir4_w(m_uart_irq_pending & m_uart_irq_mask ? 1 : 0);
+}
+
+template <unsigned N> void pc98_base_state::update_uart_irq(int state)
+{
+	if (state)
+		m_uart_irq_pending |= 1 << N;
+	else
+		m_uart_irq_pending &= ~1 << N;
+	uart_irq_check();
+}
+
 void pc98_base_state::ppi_sys_beep_portc_w(uint8_t data)
 {
 	m_beeper->set_state(!(data & 0x08));
+	m_uart_irq_mask = data & 7;
+	uart_irq_check();
 }
 
 void pc9801vm_state::ppi_sys_dac_portc_w(uint8_t data)
@@ -1668,6 +1685,8 @@ void pc9801vm_state::ppi_sys_dac_portc_w(uint8_t data)
 	// TODO: some models have a finer grained volume control at I/O port 0xae8e
 	// (98NOTE only?)
 	m_dac1bit->set_output_gain(0, m_dac1bit_disable ? 0.0 : 1.0);
+	m_uart_irq_mask = data & 7;
+	uart_irq_check();
 }
 
 /*
@@ -2228,6 +2247,23 @@ void pc9801vm_state::pc9801_ide(machine_config &config)
 	SOFTWARE_LIST(config, "cd_list").set_original("pc98_cd");
 }
 
+void pc98_base_state::pc9801_serial(machine_config &config)
+{
+	// clocked by PIT channel 2
+	I8251(config, m_sio, 0);
+	m_sio->txd_handler().set("serial", FUNC(rs232_port_device::write_txd));
+	m_sio->rts_handler().set("serial", FUNC(rs232_port_device::write_rts));
+	m_sio->dtr_handler().set("serial", FUNC(rs232_port_device::write_dtr));
+	m_sio->rxrdy_handler().set([this] (int state) { update_uart_irq<0>(state); });
+	m_sio->txempty_handler().set([this] (int state) { update_uart_irq<1>(state); });
+	m_sio->txrdy_handler().set([this] (int state) { update_uart_irq<2>(state); });
+
+	rs232_port_device &rs232(RS232_PORT(config, "serial", default_rs232_devices, nullptr));
+	rs232.rxd_handler().set(m_sio, FUNC(i8251_device::write_rxd));
+	rs232.cts_handler().set(m_sio, FUNC(i8251_device::write_cts));
+	rs232.dsr_handler().set(m_sio, FUNC(i8251_device::write_dsr));
+}
+
 void pc9801_state::pc9801_common(machine_config &config)
 {
 	PIT8253(config, m_pit, 0);
@@ -2274,7 +2310,7 @@ void pc9801_state::pc9801_common(machine_config &config)
 	pc9801_mouse(config);
 	pc9801_cbus(config);
 
-	I8251(config, m_sio, 0);
+	pc9801_serial(config);
 
 	PC9801_MEMSW(config, m_memsw, 0);
 
@@ -2292,12 +2328,12 @@ void pc9801_state::pc9801_common(machine_config &config)
 	m_screen->set_screen_update(FUNC(pc9801_state::screen_update));
 	m_screen->screen_vblank().set(FUNC(pc9801_state::vrtc_irq));
 
-	UPD7220(config, m_hgdc[0], 21.0526_MHz_XTAL / 8);
+	UPD7220(config, m_hgdc[0], 21.0526_MHz_XTAL / 8, "screen");
 	m_hgdc[0]->set_addrmap(0, &pc9801_state::upd7220_1_map);
 	m_hgdc[0]->set_draw_text(FUNC(pc9801_state::hgdc_draw_text));
 	m_hgdc[0]->vsync_wr_callback().set(m_hgdc[1], FUNC(upd7220_device::ext_sync_w));
 
-	UPD7220(config, m_hgdc[1], 21.0526_MHz_XTAL / 8);
+	UPD7220(config, m_hgdc[1], 21.0526_MHz_XTAL / 8, "screen");
 	m_hgdc[1]->set_addrmap(0, &pc9801_state::upd7220_2_map);
 	m_hgdc[1]->set_display_pixels(FUNC(pc9801_state::hgdc_display_pixels));
 
diff --git a/src/mame/nec/pc9801.h b/src/mame/nec/pc9801.h
index 5f7c017c240..895963ad372 100644
--- a/src/mame/nec/pc9801.h
+++ b/src/mame/nec/pc9801.h
@@ -33,6 +33,7 @@
 #include "machine/upd4991a.h"
 #include "machine/upd765.h"
 
+#include "bus/rs232/rs232.h"
 #include "bus/scsi/pc9801_sasi.h"
 #include "bus/scsi/scsi.h"
 #include "bus/scsi/scsihd.h"
@@ -71,7 +72,6 @@
 #include "formats/nfd_dsk.h"
 
 #define RTC_TAG      "rtc"
-#define UPD8251_TAG  "upd8251"
 #define SASIBUS_TAG  "sasi"
 
 #define ATTRSEL_REG 0
@@ -98,6 +98,7 @@ public:
 		, m_ppi_sys(*this, "ppi_sys")
 		, m_ppi_prn(*this, "ppi_prn")
 		, m_beeper(*this, "beeper")
+		, m_sio(*this, "sio")
 	{
 	}
 
@@ -112,13 +113,20 @@ protected:
 	required_device<i8255_device> m_ppi_sys;
 	required_device<i8255_device> m_ppi_prn;
 	optional_device<beep_device> m_beeper;
+	required_device<i8251_device> m_sio;
 
 	void rtc_w(uint8_t data);
 	void ppi_sys_beep_portc_w(uint8_t data);
 
+	virtual void uart_irq_check() = 0;
+	template <unsigned N> void update_uart_irq(int state);
+
+	void pc9801_serial(machine_config &config);
+
 	static void floppy_formats(format_registration &fr);
 
 	u8 m_sys_type = 0;
+	u8 m_uart_irq_mask = 0, m_uart_irq_pending = 0;
 };
 
 class pc9801_state : public pc98_base_state
@@ -142,7 +150,6 @@ public:
 		, m_pic1(*this, "pic8259_master")
 		, m_pic2(*this, "pic8259_slave")
 		, m_memsw(*this, "memsw")
-		, m_sio(*this, UPD8251_TAG)
 		, m_sasibus(*this, SASIBUS_TAG)
 		, m_sasi_data_out(*this, "sasi_data_out")
 		, m_sasi_data_in(*this, "sasi_data_in")
@@ -175,7 +182,6 @@ protected:
 	required_device<pic8259_device> m_pic2;
 private:
 	required_device<pc9801_memsw_device> m_memsw;
-	required_device<i8251_device> m_sio;
 	optional_device<scsi_port_device> m_sasibus;
 	optional_device<output_latch_device> m_sasi_data_out;
 	optional_device<input_buffer_device> m_sasi_data_in;
@@ -352,6 +358,10 @@ private:
 	void ppi_mouse_portc_w(uint8_t data);
 
 	TIMER_DEVICE_CALLBACK_MEMBER( mouse_irq_cb );
+
+// UART SIO
+protected:
+	virtual void uart_irq_check() override;
 };
 
 /**********************************************************
diff --git a/src/mame/nec/pc98ha.cpp b/src/mame/nec/pc98ha.cpp
index d6e9814a7a5..21110ec1bc3 100644
--- a/src/mame/nec/pc98ha.cpp
+++ b/src/mame/nec/pc98ha.cpp
@@ -151,7 +151,8 @@ void pc98lt_state::lt_io(address_map &map)
 	map.unmap_value_high();
 //  map(0x0000, 0x001f) // PIC (bit 3 ON slave / master), V50 internal / <undefined>
 	map(0x0020, 0x002f).w(FUNC(pc98lt_state::rtc_w)).umask16(0x00ff);
-	map(0x0030, 0x0037).rw(m_ppi_sys, FUNC(i8255_device::read), FUNC(i8255_device::write)).umask16(0xff00); //i8251 RS232c / i8255 system port
+	map(0x0030, 0x0037).rw(m_ppi_sys, FUNC(i8255_device::read), FUNC(i8255_device::write)).umask16(0xff00);
+	map(0x0030, 0x0033).rw(m_sio, FUNC(i8251_device::read), FUNC(i8251_device::write)).umask16(0x00ff); //i8251 RS232c / i8255 system port
 	map(0x0040, 0x0047).rw(m_ppi_prn, FUNC(i8255_device::read), FUNC(i8255_device::write)).umask16(0x00ff);
 	map(0x0040, 0x0047).rw(m_keyb, FUNC(pc9801_kbd_device::rx_r), FUNC(pc9801_kbd_device::tx_w)).umask16(0xff00); //i8255 printer port / i8251 keyboard
 //  map(0x0070, 0x007f) // PIT, V50 internal
@@ -418,6 +419,13 @@ static void pc9801_floppies(device_slot_interface &device)
 //  device.option_add("35hd", FLOPPY_35_HD);
 }
 
+void pc98lt_state::uart_irq_check()
+{
+	m_maincpu->set_input_line(4, m_uart_irq_pending & m_uart_irq_mask ? ASSERT_LINE : CLEAR_LINE);
+}
+
+
+
 void pc98lt_state::lt_config(machine_config &config)
 {
 	const XTAL xtal = XTAL(8'000'000);
@@ -427,10 +435,9 @@ void pc98lt_state::lt_config(machine_config &config)
 	// TODO: jumps off the weeds if divided by / 4 after timer check, DMA issue?
 //  m_maincpu->set_tclk(xtal / 4);
 	m_maincpu->set_tclk(xtal / 100);
-//  m_maincpu->tout2_cb().set_inputline(m_maincpu, INPUT_LINE_IRQ2);
 //  m_pit->out_handler<0>().set(m_pic1, FUNC(pic8259_device::ir0_w));
-//  m_pit->out_handler<2>().set(m_sio, FUNC(i8251_device::write_txc));
-//  m_pit->out_handler<2>().append(m_sio, FUNC(i8251_device::write_rxc));
+	m_maincpu->tout2_cb().set(m_sio, FUNC(i8251_device::write_txc));
+	m_maincpu->tout2_cb().append(m_sio, FUNC(i8251_device::write_rxc));
 
 //  m_maincpu->set_irq_acknowledge_callback("pic8259_master", FUNC(pic8259_device::inta_cb));
 
@@ -444,6 +451,8 @@ void pc98lt_state::lt_config(machine_config &config)
 //  m_ppi_sys->in_pc_callback().set_constant(0xa0); // 0x80 cpu triple fault reset flag?
 	m_ppi_sys->out_pc_callback().set(FUNC(pc98lt_state::ppi_sys_beep_portc_w));
 
+	pc9801_serial(config);
+
 	I8255(config, m_ppi_prn, 0);
 	m_ppi_prn->in_pb_callback().set_ioport("PRNB");
 
diff --git a/src/mame/nec/pc98ha.h b/src/mame/nec/pc98ha.h
index 63b1cb1477a..e872fd03904 100644
--- a/src/mame/nec/pc98ha.h
+++ b/src/mame/nec/pc98ha.h
@@ -64,6 +64,8 @@ private:
 
 	u8 m_floppy_mode = 0;
 	u8 m_fdc_ctrl = 0;
+
+	virtual void uart_irq_check() override;
 };
 
 class pc98ha_state : public pc98lt_state
diff --git a/src/mame/nec/pc_h98.cpp b/src/mame/nec/pc_h98.cpp
index 001912b1904..663a8e22294 100644
--- a/src/mame/nec/pc_h98.cpp
+++ b/src/mame/nec/pc_h98.cpp
@@ -44,6 +44,7 @@ void pc_hyper98_state::pc_h98_io(address_map &map)
 {
 	pc_hyper98_state::pc9801bx2_io(map);
 	// ...
+//  map(0x4*a*, 0x4*a*) μPD72120 "AGDC"
 }
 
 // TODO: backported from pc9801_epson.cpp, needs mods