diff --git a/src/emu/bus/ql/cst_q_plus4.c b/src/emu/bus/ql/cst_q_plus4.c
index b75e8214ed9..7b98a3319b3 100644
--- a/src/emu/bus/ql/cst_q_plus4.c
+++ b/src/emu/bus/ql/cst_q_plus4.c
@@ -13,6 +13,14 @@
 
 
 
+//**************************************************************************
+//  MACROS/CONSTANTS
+//**************************************************************************
+
+#define MC6821_TAG "mc6821"
+
+
+
 //**************************************************************************
 //  DEVICE DEFINITIONS
 //**************************************************************************
@@ -40,6 +48,38 @@ const rom_entry *cst_q_plus4_t::device_rom_region() const
 }
 
 
+//-------------------------------------------------
+//  MACHINE_CONFIG_FRAGMENT( cst_q_plus4 )
+//-------------------------------------------------
+
+static MACHINE_CONFIG_FRAGMENT( cst_q_plus4 )
+	MCFG_DEVICE_ADD(MC6821_TAG, PIA6821, 0)
+
+	MCFG_QL_EXPANSION_SLOT_ADD("exp1", ql_expansion_cards, NULL)
+	MCFG_QL_EXPANSION_SLOT_EXTINTL_CALLBACK(WRITELINE(cst_q_plus4_t, exp1_extintl_w))
+
+	MCFG_QL_EXPANSION_SLOT_ADD("exp2", ql_expansion_cards, NULL)
+	MCFG_QL_EXPANSION_SLOT_EXTINTL_CALLBACK(WRITELINE(cst_q_plus4_t, exp2_extintl_w))
+
+	MCFG_QL_EXPANSION_SLOT_ADD("exp3", ql_expansion_cards, NULL)
+	MCFG_QL_EXPANSION_SLOT_EXTINTL_CALLBACK(WRITELINE(cst_q_plus4_t, exp3_extintl_w))
+
+	MCFG_QL_EXPANSION_SLOT_ADD("exp4", ql_expansion_cards, NULL)
+	MCFG_QL_EXPANSION_SLOT_EXTINTL_CALLBACK(WRITELINE(cst_q_plus4_t, exp4_extintl_w))
+MACHINE_CONFIG_END
+
+
+//-------------------------------------------------
+//  machine_config_additions - device-specific
+//  machine configurations
+//-------------------------------------------------
+
+machine_config_constructor cst_q_plus4_t::device_mconfig_additions() const
+{
+	return MACHINE_CONFIG_NAME( cst_q_plus4 );
+}
+
+
 
 //**************************************************************************
 //  LIVE DEVICE
@@ -51,7 +91,16 @@ const rom_entry *cst_q_plus4_t::device_rom_region() const
 
 cst_q_plus4_t::cst_q_plus4_t(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock) :
 	device_t(mconfig, CST_Q_PLUS4, "CST Q+4", tag, owner, clock, "ql_qplus4", __FILE__),
-	device_ql_expansion_card_interface(mconfig, *this)
+	device_ql_expansion_card_interface(mconfig, *this),
+	m_exp1(*this, "exp1"),
+	m_exp2(*this, "exp2"),
+	m_exp3(*this, "exp3"),
+	m_exp4(*this, "exp4"),
+	m_rom(*this, "rom"),
+	m_exp1_extinl(CLEAR_LINE),
+	m_exp2_extinl(CLEAR_LINE),
+	m_exp3_extinl(CLEAR_LINE),
+	m_exp4_extinl(CLEAR_LINE)
 {
 }
 
@@ -71,6 +120,16 @@ void cst_q_plus4_t::device_start()
 
 UINT8 cst_q_plus4_t::read(address_space &space, offs_t offset, UINT8 data)
 {
+	if (offset >= 0xc000 && offset < 0xc200)
+	{
+		data = m_rom->base()[offset & 0x1fff];
+	}
+
+	data = m_exp1->read(space, offset, data);
+	data = m_exp2->read(space, offset, data);
+	data = m_exp3->read(space, offset, data);
+	data = m_exp4->read(space, offset, data);
+
 	return data;
 }
 
@@ -81,4 +140,8 @@ UINT8 cst_q_plus4_t::read(address_space &space, offs_t offset, UINT8 data)
 
 void cst_q_plus4_t::write(address_space &space, offs_t offset, UINT8 data)
 {
+	m_exp1->write(space, offset, data);
+	m_exp2->write(space, offset, data);
+	m_exp3->write(space, offset, data);
+	m_exp4->write(space, offset, data);
 }
diff --git a/src/emu/bus/ql/cst_q_plus4.h b/src/emu/bus/ql/cst_q_plus4.h
index da66d6c4d02..ad6b385782a 100644
--- a/src/emu/bus/ql/cst_q_plus4.h
+++ b/src/emu/bus/ql/cst_q_plus4.h
@@ -15,6 +15,7 @@
 #define __CST_Q_PLUS4__
 
 #include "exp.h"
+#include "machine/6821pia.h"
 
 
 
@@ -34,6 +35,12 @@ public:
 
 	// optional information overrides
 	virtual const rom_entry *device_rom_region() const;
+	virtual machine_config_constructor device_mconfig_additions() const;
+
+	DECLARE_WRITE_LINE_MEMBER( exp1_extintl_w ) { m_exp1_extinl = state; update_extintl(); }
+	DECLARE_WRITE_LINE_MEMBER( exp2_extintl_w ) { m_exp2_extinl = state; update_extintl(); }
+	DECLARE_WRITE_LINE_MEMBER( exp3_extintl_w ) { m_exp3_extinl = state; update_extintl(); }
+	DECLARE_WRITE_LINE_MEMBER( exp4_extintl_w ) { m_exp4_extinl = state; update_extintl(); }
 
 protected:
 	// device-level overrides
@@ -44,6 +51,18 @@ protected:
 	virtual void write(address_space &space, offs_t offset, UINT8 data);
 
 private:
+	void update_extintl() { m_slot->extintl_w(m_exp1_extinl || m_exp2_extinl || m_exp3_extinl || m_exp4_extinl); }
+
+	required_device<ql_expansion_slot_t> m_exp1;
+	required_device<ql_expansion_slot_t> m_exp2;
+	required_device<ql_expansion_slot_t> m_exp3;
+	required_device<ql_expansion_slot_t> m_exp4;
+	required_memory_region m_rom;
+
+	int m_exp1_extinl;
+	int m_exp2_extinl;
+	int m_exp3_extinl;
+	int m_exp4_extinl;
 };