diff --git a/scripts/src/bus.lua b/scripts/src/bus.lua
index 5550ff2e396..eee10688f64 100644
--- a/scripts/src/bus.lua
+++ b/scripts/src/bus.lua
@@ -1585,6 +1585,8 @@ if (BUSES["ISA"]~=null) then
 		MAME_DIR .. "src/devices/bus/isa/asc88.h",
 		MAME_DIR .. "src/devices/bus/isa/bblue2.cpp",
 		MAME_DIR .. "src/devices/bus/isa/bblue2.h",
+		MAME_DIR .. "src/devices/bus/isa/3xtwin.cpp",
+		MAME_DIR .. "src/devices/bus/isa/3xtwin.h",
 	}
 end
 
diff --git a/scripts/src/machine.lua b/scripts/src/machine.lua
index 012119a8a7e..8d4069947f0 100644
--- a/scripts/src/machine.lua
+++ b/scripts/src/machine.lua
@@ -983,6 +983,18 @@ if (MACHINES["CHESSMACHINE"]~=null) then
 end
 
 
+---------------------------------------------------
+--
+--@src/devices/machine/com52c50.h,MACHINES["COM52C50"] = true
+---------------------------------------------------
+
+if (MACHINES["COM52C50"]~=null) then
+	files {
+		MAME_DIR .. "src/devices/machine/com52c50.cpp",
+		MAME_DIR .. "src/devices/machine/com52c50.h",
+	}
+end
+
 ---------------------------------------------------
 --
 --@src/devices/machine/com8116.h,MACHINES["COM8116"] = true
diff --git a/scripts/target/mame/arcade.lua b/scripts/target/mame/arcade.lua
index 75ef61332ee..6b40790f785 100644
--- a/scripts/target/mame/arcade.lua
+++ b/scripts/target/mame/arcade.lua
@@ -463,6 +463,7 @@ MACHINES["CDP1871"] = true
 MACHINES["CHESSMACHINE"] = true
 MACHINES["CMOS40105"] = true
 MACHINES["CDU76S"] = true
+MACHINES["COM52C50"] = true
 MACHINES["COM8116"] = true
 MACHINES["CR589"] = true
 --MACHINES["CS4031"] = true
diff --git a/scripts/target/mame/mess.lua b/scripts/target/mame/mess.lua
index e96b17cf4b7..b584cbaebe2 100644
--- a/scripts/target/mame/mess.lua
+++ b/scripts/target/mame/mess.lua
@@ -483,6 +483,7 @@ MACHINES["CDP1879"] = true
 --MACHINES["CDU76S"] = true
 MACHINES["CHESSMACHINE"] = true
 MACHINES["CMOS40105"] = true
+MACHINES["COM52C50"] = true
 MACHINES["COM8116"] = true
 MACHINES["COP452"] = true
 MACHINES["CR589"] = true
diff --git a/src/devices/bus/isa/3xtwin.cpp b/src/devices/bus/isa/3xtwin.cpp
new file mode 100644
index 00000000000..b30c83ab1ce
--- /dev/null
+++ b/src/devices/bus/isa/3xtwin.cpp
@@ -0,0 +1,95 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+/***************************************************************************
+
+    Emerald Technology Inc. 3XTwin IBM 5251/11 twinax emulation board
+
+    This smallish card is rather tightly packed with DIP ICs (mostly simple
+    LSTTL and a few line drivers/receivers) to the point where their
+    location numbers are difficult to read. There is no host BIOS, and the
+    65C02's "TWINMON" firmware does very little, clearly relying on
+    external software.
+
+    Communication between the host system and local CPU seems to take place
+    via shared access to a KM62256LP-10 SRAM.
+
+***************************************************************************/
+
+#include "emu.h"
+#include "3xtwin.h"
+
+#include "cpu/m6502/r65c02.h"
+#include "machine/com52c50.h"
+
+
+// device type definition
+DEFINE_DEVICE_TYPE(ISA8_3XTWIN, isa8_3xtwin_device, "3xtwin", "Emerald Technology 3XTwin Twinax Emulation Card")
+
+isa8_3xtwin_device::isa8_3xtwin_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock)
+	: device_t(mconfig, ISA8_3XTWIN, tag, owner, clock)
+	, device_isa8_card_interface(mconfig, *this)
+{
+}
+
+void isa8_3xtwin_device::device_start()
+{
+}
+
+void isa8_3xtwin_device::mpu_map(address_map &map)
+{
+	map(0x0000, 0x1fff).ram();
+	map(0x2000, 0x2007).m("tic", FUNC(com52c50_device::map));
+	map(0x4000, 0xbfff).ram();
+	map(0xe000, 0xffff).rom().region("firmware", 0);
+}
+
+
+static INPUT_PORTS_START(3xtwin)
+	PORT_START("IOBASE")
+	PORT_DIPNAME(0x1f, 0x19, "Base I/O Address") PORT_DIPLOCATION("S1:5,4,3,2,1")
+	PORT_DIPSETTING(0x10, "200")
+	PORT_DIPSETTING(0x11, "220")
+	PORT_DIPSETTING(0x12, "240")
+	PORT_DIPSETTING(0x13, "260")
+	PORT_DIPSETTING(0x14, "280")
+	PORT_DIPSETTING(0x15, "2A0")
+	PORT_DIPSETTING(0x16, "2C0")
+	PORT_DIPSETTING(0x17, "2E0")
+	PORT_DIPSETTING(0x18, "300")
+	PORT_DIPSETTING(0x19, "320")
+	PORT_DIPSETTING(0x1a, "340")
+	PORT_DIPSETTING(0x1b, "360")
+	PORT_DIPSETTING(0x1c, "380")
+	PORT_DIPSETTING(0x1d, "3A0")
+	PORT_DIPSETTING(0x1e, "3C0")
+	PORT_DIPSETTING(0x1f, "3E0")
+
+	// TODO: IRQ jumpers
+INPUT_PORTS_END
+
+ioport_constructor isa8_3xtwin_device::device_input_ports() const
+{
+	return INPUT_PORTS_NAME(3xtwin);
+}
+
+void isa8_3xtwin_device::device_add_mconfig(machine_config &config)
+{
+	r65c02_device &mpu(R65C02(config, "mpu", 16_MHz_XTAL / 4)); // R65C02P4
+	mpu.set_addrmap(AS_PROGRAM, &isa8_3xtwin_device::mpu_map);
+
+	com52c50_device &tic(COM52C50(config, "tic", 16_MHz_XTAL));
+	tic.int1_callback().set_inputline("mpu", r65c02_device::IRQ_LINE);
+	tic.int2_callback().set_inputline("mpu", r65c02_device::NMI_LINE);
+}
+
+ROM_START(3xtwin)
+	ROM_REGION(0x2000, "firmware", 0) // "MON VER E.01"
+	ROM_LOAD("370906502.u2", 0x0000, 0x2000, CRC(d4157bc4) SHA1(359428ce0047f9192a44790c8670af956cf6ed70))
+
+	// PLDs (undumped) marked "TWINCLK" (U9: ULC24/22V10-15) and "TWINLGC" (U12: PAL20L10ACNS)
+ROM_END
+
+const tiny_rom_entry *isa8_3xtwin_device::device_rom_region() const
+{
+	return ROM_NAME(3xtwin);
+}
diff --git a/src/devices/bus/isa/3xtwin.h b/src/devices/bus/isa/3xtwin.h
new file mode 100644
index 00000000000..cb9aeb286eb
--- /dev/null
+++ b/src/devices/bus/isa/3xtwin.h
@@ -0,0 +1,40 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+/***************************************************************************
+
+    Emerald Technology Inc. 3XTwin IBM 5251/11 emulation board
+
+***************************************************************************/
+
+#ifndef MAME_BUS_ISA_3XTWIN_H
+#define MAME_BUS_ISA_3XTWIN_H
+
+#pragma once
+
+#include "isa.h"
+
+
+// ======================> isa8_3xtwin_device
+
+class isa8_3xtwin_device : public device_t, public device_isa8_card_interface
+{
+public:
+	// device type constructor
+	isa8_3xtwin_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock);
+
+protected:
+	// device-level overrides
+	virtual void device_start() override;
+	virtual ioport_constructor device_input_ports() const override;
+	virtual void device_add_mconfig(machine_config &config) override;
+	virtual const tiny_rom_entry *device_rom_region() const override;
+
+private:
+	// local memory map
+	void mpu_map(address_map &map);
+};
+
+// device type declaration
+DECLARE_DEVICE_TYPE(ISA8_3XTWIN, isa8_3xtwin_device)
+
+#endif // MAME_BUS_ISA_3XTWIN_H
diff --git a/src/devices/bus/isa/isa_cards.cpp b/src/devices/bus/isa/isa_cards.cpp
index 8f1232dcd13..ce23388ea1d 100644
--- a/src/devices/bus/isa/isa_cards.cpp
+++ b/src/devices/bus/isa/isa_cards.cpp
@@ -72,6 +72,7 @@
 #include "eis_sad8852.h"
 #include "eis_twib.h"
 #include "np600.h"
+#include "3xtwin.h"
 
 // communication ports
 #include "lpt.h"
@@ -138,6 +139,7 @@ void pc_isa8_cards(device_slot_interface &device)
 	device.option_add("epc_twib", ISA8_EIS_TWIB);
 	device.option_add("babyblue2", ISA8_BABYBLUE2);
 	device.option_add("acb2072", ACB2072);
+	device.option_add("3xtwin", ISA8_3XTWIN);
 }
 
 void pc_isa16_cards(device_slot_interface &device)
@@ -183,6 +185,7 @@ void pc_isa16_cards(device_slot_interface &device)
 	device.option_add("epc_twib", ISA8_EIS_TWIB);
 	device.option_add("babyblue2", ISA8_BABYBLUE2);
 	device.option_add("acb2072", ACB2072);
+	device.option_add("3xtwin", ISA8_3XTWIN);
 	// 16-bit
 	device.option_add("ide", ISA16_IDE);
 	device.option_add("ne2000", NE2000);
diff --git a/src/devices/machine/com52c50.cpp b/src/devices/machine/com52c50.cpp
new file mode 100644
index 00000000000..89b4e176f85
--- /dev/null
+++ b/src/devices/machine/com52c50.cpp
@@ -0,0 +1,165 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+/***************************************************************************
+
+    Standard Microsystems Corp. COM52C50 Twinax Interface Circuit (TIC)
+
+    Skeleton device.
+
+***************************************************************************/
+
+#include "emu.h"
+#include "com52c50.h"
+
+
+// device type definition
+DEFINE_DEVICE_TYPE(COM52C50, com52c50_device, "com52c50", "SMC COM52C50 TIC")
+
+com52c50_device::com52c50_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock)
+	: device_t(mconfig, COM52C50, tag, owner, clock)
+	, m_int1_callback(*this)
+	, m_int2_callback(*this)
+	, m_rx_dma_callback(*this)
+	, m_tx_dma_callback(*this)
+	, m_int_mask(0)
+	, m_int_status(0)
+	, m_zero_fill(0)
+	, m_present_address(0)
+	, m_rx_status(0)
+	, m_tx_status(0)
+	, m_control(0)
+	, m_mode(0)
+{
+}
+
+void com52c50_device::map(address_map &map)
+{
+	map(0, 0).w(FUNC(com52c50_device::mode_w));
+	map(1, 1).rw(FUNC(com52c50_device::int_status_r), FUNC(com52c50_device::int_mask_w));
+	map(2, 2).rw(FUNC(com52c50_device::rx_status_r), FUNC(com52c50_device::address_select_w));
+	map(3, 3).rw(FUNC(com52c50_device::rx_buffer_r), FUNC(com52c50_device::control_w));
+	map(4, 4).w(FUNC(com52c50_device::zero_fill_w));
+	map(5, 5).rw(FUNC(com52c50_device::present_address_r), FUNC(com52c50_device::present_address_w));
+	map(6, 6).mirror(1).r(FUNC(com52c50_device::tx_status_r));
+	map(6, 6).w(FUNC(com52c50_device::tx_buffer_w));
+	map(7, 7).w(FUNC(com52c50_device::tx_buffer_eom_w));
+}
+
+void com52c50_device::device_resolve_objects()
+{
+	m_int1_callback.resolve_safe();
+	m_int2_callback.resolve_safe();
+	m_rx_dma_callback.resolve_safe();
+	m_tx_dma_callback.resolve_safe();
+}
+
+void com52c50_device::device_start()
+{
+	save_item(NAME(m_int_mask));
+	save_item(NAME(m_int_status));
+	save_item(NAME(m_zero_fill));
+	save_item(NAME(m_present_address));
+	save_item(NAME(m_rx_status));
+	save_item(NAME(m_tx_status));
+	save_item(NAME(m_control));
+	save_item(NAME(m_mode));
+}
+
+void com52c50_device::device_reset()
+{
+	m_int_mask = 0;
+	m_int_status = 0;
+	m_zero_fill = 0;
+	m_rx_status = 0;
+	m_tx_status = 0;
+	m_control = 0x01;
+	m_mode = 0;
+
+	m_int1_callback(CLEAR_LINE);
+	m_int2_callback(CLEAR_LINE);
+}
+
+u8 com52c50_device::rx_buffer_r()
+{
+	if (!machine().side_effects_disabled())
+		logerror("%s: Reading data from RX buffer\n", machine().describe_context());
+	return 0;
+}
+
+void com52c50_device::tx_buffer_w(u8 data)
+{
+	logerror("%s: Writing %02X to TX buffer\n", machine().describe_context(), data);
+}
+
+void com52c50_device::tx_buffer_eom_w(u8 data)
+{
+	logerror("%s: Writing %02X to TX buffer EOM\n", machine().describe_context(), data);
+}
+
+void com52c50_device::zero_fill_w(u8 data)
+{
+	logerror("%s: Writing %02X to zero fill register\n", machine().describe_context(), data);
+	m_zero_fill = data;
+}
+
+void com52c50_device::int_mask_w(u8 data)
+{
+	logerror("%s: Writing %02X to interrupt mask register\n", machine().describe_context(), data);
+	m_int_mask = data;
+}
+
+void com52c50_device::address_select_w(u8 data)
+{
+	logerror("%s: Writing %02X to address select register\n", machine().describe_context(), data);
+}
+
+u8 com52c50_device::present_address_r()
+{
+	return m_present_address;
+}
+
+void com52c50_device::present_address_w(u8 data)
+{
+	logerror("%s: Writing %02X to present address register\n", machine().describe_context(), data);
+	m_present_address = data & 0x07;
+}
+
+u8 com52c50_device::int_status_r()
+{
+	return m_int_status;
+}
+
+u8 com52c50_device::rx_status_r()
+{
+	return m_rx_status | (m_present_address << 1);
+}
+
+u8 com52c50_device::tx_status_r()
+{
+	return m_tx_status;
+}
+
+void com52c50_device::control_w(u8 data)
+{
+	if (!BIT(data, 0))
+	{
+		logerror("%s: Software reset\n", machine().describe_context());
+
+		m_int_mask = 0;
+		m_int_status = 0;
+		m_zero_fill = 0;
+		m_rx_status = 0;
+		m_tx_status = 0;
+		m_mode = 0;
+	}
+
+	logerror("%s: Writing %02X to control register\n", machine().describe_context(), data);
+	m_control = data;
+}
+
+void com52c50_device::mode_w(u8 data)
+{
+	logerror("%s: Writing %02X to mode register\n", machine().describe_context(), data);
+	m_mode = data;
+}
+
diff --git a/src/devices/machine/com52c50.h b/src/devices/machine/com52c50.h
new file mode 100644
index 00000000000..085a3e0808a
--- /dev/null
+++ b/src/devices/machine/com52c50.h
@@ -0,0 +1,89 @@
+// license:BSD-3-Clause
+// copyright-holders:AJR
+/***************************************************************************
+
+    Standard Microsystems Corp. COM52C50 Twinax Interface Circuit (TIC)
+
+****************************************************************************
+                           _____    _____
+                   D2   1 |*    \__/     | 28  Vcc
+                   D3   2 |              | 27  D1
+                  /WR   3 |              | 26  D0
+                /TXEN   4 |              | 25  /CS
+                 /DTX   5 |              | 24  /RD
+                   TX   6 |              | 23  A0
+               TX DMA   7 |              | 22  A1
+                   RX   8 |   COM52C50   | 21  A2
+                   D4   9 |              | 20  /INT1
+                   D5  10 |              | 19  /INT2
+               /RESET  11 |              | 18  RX DMA
+                XTAL2  12 |              | 17  CLKOUT
+                XTAL1  13 |              | 16  D7
+                  GND  14 |______________| 15  D6
+
+***************************************************************************/
+
+#ifndef MAME_MACHINE_COM52C50_H
+#define MAME_MACHINE_COM52C50_H
+
+#pragma once
+
+
+// ======================> com52c50_device
+
+class com52c50_device : public device_t
+{
+public:
+	// device type constructor
+	com52c50_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock);
+
+	// callback configuration
+	auto int1_callback() { return m_int1_callback.bind(); }
+	auto int2_callback() { return m_int2_callback.bind(); }
+	auto rx_dma_callback() { return m_rx_dma_callback.bind(); }
+	auto tx_dma_callback() { return m_tx_dma_callback.bind(); }
+
+	// bus interface
+	u8 rx_buffer_r();
+	void tx_buffer_w(u8 data);
+	void tx_buffer_eom_w(u8 data);
+	void zero_fill_w(u8 data);
+	void int_mask_w(u8 data);
+	void address_select_w(u8 data);
+	u8 present_address_r();
+	void present_address_w(u8 data);
+	u8 int_status_r();
+	u8 rx_status_r();
+	u8 tx_status_r();
+	void control_w(u8 data);
+	void mode_w(u8 data);
+	void map(address_map &map);
+
+protected:
+	// device-level overrides
+	virtual void device_resolve_objects() override;
+	virtual void device_start() override;
+	virtual void device_reset() override;
+
+private:
+	// device callbacks
+	devcb_write_line m_int1_callback;
+	devcb_write_line m_int2_callback;
+	devcb_write_line m_rx_dma_callback;
+	devcb_write_line m_tx_dma_callback;
+
+	// internal state
+	u8 m_int_mask;
+	u8 m_int_status;
+	u8 m_zero_fill;
+	u8 m_present_address;
+	u8 m_rx_status;
+	u8 m_tx_status;
+	u8 m_control;
+	u8 m_mode;
+};
+
+// device type declaration
+DECLARE_DEVICE_TYPE(COM52C50, com52c50_device)
+
+#endif // MAME_MACHINE_COM52C50_H