Don't need a trampoline for these and added bare-bones SCI

src/devices/cpu/sh2/sh7604_bus.cpp

@@ -150,20 +150,10 @@ void sh7604_bus_device::device_reset()
 //  READ/WRITE HANDLERS
 //**************************************************************************
 
-inline void sh7604_bus_device::writeword(offs_t address, UINT16 data)
-{
-	space().write_word(address, data);
-}
-
-inline UINT16 sh7604_bus_device::readword(offs_t address)
-{
-	return space().read_word(address);
-}
-
 READ32_MEMBER( sh7604_bus_device::read )
 {
 	// 16 bit access only, TODO
-	return readword(offset);
+	return space.read_word(offset) & 0xffff;
 }
 
 WRITE32_MEMBER( sh7604_bus_device::write )
@@ -177,5 +167,5 @@ WRITE32_MEMBER( sh7604_bus_device::write )
 			throw emu_fatalerror("%s: making bus write with ID signature = %04x!\n", tag(),data >> 16);
 	}
 	
-	writeword(offset,data & 0xffff);
+	space.write_word(offset,data & 0xffff);
 }

src/devices/cpu/sh2/sh7604_bus.h

@@ -61,8 +61,6 @@ protected:
 private:
 	bool m_is_slave;
 	const address_space_config      m_space_config;
-	void writeword(offs_t address, UINT16 data);
-	UINT16 readword(offs_t address);
 	
 	UINT16 m_bcr1;
 	UINT16 m_bcr2;

src/devices/cpu/sh2/sh7604_sci.cpp

@@ -0,0 +1,78 @@
+// license:BSD-3-Clause
+// copyright-holders:<author_name>
+/***************************************************************************
+
+Template for skeleton device
+
+***************************************************************************/
+
+#include "emu.h"
+#include "sh7604_sci.h"
+
+
+
+//**************************************************************************
+//  GLOBAL VARIABLES
+//**************************************************************************
+
+// device type definition
+const device_type SH7604_SCI = &device_creator<sh7604_sci_device>;
+
+
+//**************************************************************************
+//  LIVE DEVICE
+//**************************************************************************
+
+static ADDRESS_MAP_START( sci_regs, AS_0, 8, sh7604_sci_device )
+
+ADDRESS_MAP_END
+
+//-------------------------------------------------
+//  sh7604_sci_device - constructor
+//-------------------------------------------------
+
+sh7604_sci_device::sh7604_sci_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock)
+	: device_t(mconfig, SH7604_SCI, "sh7604_sci_longname", tag, owner, clock, "sh7604_sci", __FILE__),
+	device_memory_interface(mconfig, *this),
+	m_space_config("regs", ENDIANNESS_BIG, 8, 4, 0, nullptr, *ADDRESS_MAP_NAME(sci_regs))
+
+{
+}
+
+
+const address_space_config *sh7604_sci_device::memory_space_config(address_spacenum spacenum) const
+{
+	return (spacenum == AS_0) ? &m_space_config : nullptr;
+}
+
+//-------------------------------------------------
+//  device_start - device-specific startup
+//-------------------------------------------------
+
+void sh7604_sci_device::device_start()
+{
+}
+
+
+//-------------------------------------------------
+//  device_reset - device-specific reset
+//-------------------------------------------------
+
+void sh7604_sci_device::device_reset()
+{
+}
+
+
+//**************************************************************************
+//  READ/WRITE HANDLERS
+//**************************************************************************
+
+READ8_MEMBER( sh7604_sci_device::read )
+{
+	return space.read_byte(offset);
+}
+
+WRITE8_MEMBER( sh7604_sci_device::write )
+{
+	space.write_byte(offset,data);
+}

src/devices/cpu/sh2/sh7604_sci.h

@@ -0,0 +1,62 @@
+// license:BSD-3-Clause
+// copyright-holders:<author_name>
+/***************************************************************************
+
+Template for skeleton device
+
+***************************************************************************/
+
+#pragma once
+
+#ifndef __SH7604_SCIDEV_H__
+#define __SH7604_SCIDEV_H__
+
+
+
+//**************************************************************************
+//  INTERFACE CONFIGURATION MACROS
+//**************************************************************************
+
+#define MCFG_SH7604_SCI_ADD(_tag,_freq) \
+	MCFG_DEVICE_ADD(_tag, SH7604_SCI, _freq)
+
+//**************************************************************************
+//  TYPE DEFINITIONS
+//**************************************************************************
+
+// ======================> sh7604_sci_device
+
+class sh7604_sci_device : public device_t,
+    					  public device_memory_interface
+{
+public:
+	// construction/destruction
+	sh7604_sci_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock);
+
+	// I/O operations
+	DECLARE_WRITE8_MEMBER( write );
+	DECLARE_READ8_MEMBER( read );
+
+	virtual const address_space_config *memory_space_config(address_spacenum spacenum = AS_0) const override;
+protected:
+	// device-level overrides
+//	virtual void device_validity_check(validity_checker &valid) const;
+	virtual void device_start() override;
+	virtual void device_reset() override;
+private:
+	const address_space_config      m_space_config;
+};
+
+
+// device type definition
+extern const device_type SH7604_SCI;
+
+
+
+//**************************************************************************
+//  GLOBAL VARIABLES
+//**************************************************************************
+
+
+
+#endif