diff --git a/src/emu/machine/mos6551.c b/src/emu/machine/mos6551.c
index 1ad74f3dafc..63436791ddd 100644
--- a/src/emu/machine/mos6551.c
+++ b/src/emu/machine/mos6551.c
@@ -345,6 +345,16 @@ void mos6551_device::set_rxc(int clock)
 }
 
 
+//-------------------------------------------------
+//  rxd_w - receive data write
+//-------------------------------------------------
+
+WRITE_LINE_MEMBER( mos6551_device::rxd_w )
+{
+	check_for_start(state);
+}
+
+
 //-------------------------------------------------
 //  rxc_w - receive clock write
 //-------------------------------------------------
diff --git a/src/emu/machine/mos6551.h b/src/emu/machine/mos6551.h
index 879311059a2..1736d61c2bb 100644
--- a/src/emu/machine/mos6551.h
+++ b/src/emu/machine/mos6551.h
@@ -76,6 +76,7 @@ public:
 	DECLARE_READ8_MEMBER( read );
 	DECLARE_WRITE8_MEMBER( write );
 
+	DECLARE_WRITE_LINE_MEMBER( rxd_w );
 	DECLARE_WRITE_LINE_MEMBER( rxc_w );
 	DECLARE_WRITE_LINE_MEMBER( cts_w );
 	DECLARE_WRITE_LINE_MEMBER( dsr_w );
diff --git a/src/mess/machine/c64_swiftlink.c b/src/mess/machine/c64_swiftlink.c
index 536181f1fd4..de64c3e2a91 100644
--- a/src/mess/machine/c64_swiftlink.c
+++ b/src/mess/machine/c64_swiftlink.c
@@ -42,11 +42,11 @@ SLOT_INTERFACE_END
 
 static const rs232_port_interface rs232_intf =
 {
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, rxd_w),
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, dcd_w),
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, dsr_w),
 	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, cts_w)
 };
 
 
@@ -56,6 +56,7 @@ static const rs232_port_interface rs232_intf =
 
 static MACHINE_CONFIG_FRAGMENT( c64_swiftlink )
 	MCFG_MOS6551_ADD(MOS6551_TAG, XTAL_3_6864MHz, DEVWRITELINE(DEVICE_SELF, c64_swiftlink_cartridge_device, acia_irq_w))
+	MCFG_MOS6551_RXD_TXD_CALLBACKS(NULL, DEVWRITELINE(RS232_TAG, rs232_port_device, tx))
 
 	MCFG_RS232_PORT_ADD(RS232_TAG, rs232_intf, rs232_devices, NULL, NULL)
 MACHINE_CONFIG_END
diff --git a/src/mess/machine/c64_turbo232.c b/src/mess/machine/c64_turbo232.c
index 6b8e9fd2c60..917323883e3 100644
--- a/src/mess/machine/c64_turbo232.c
+++ b/src/mess/machine/c64_turbo232.c
@@ -42,11 +42,11 @@ SLOT_INTERFACE_END
 
 static const rs232_port_interface rs232_intf =
 {
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, rxd_w),
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, dcd_w),
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, dsr_w),
 	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL,
-	DEVCB_NULL
+	DEVCB_DEVICE_LINE_MEMBER(MOS6551_TAG, mos6551_device, cts_w)
 };
 
 
@@ -56,6 +56,7 @@ static const rs232_port_interface rs232_intf =
 
 static MACHINE_CONFIG_FRAGMENT( c64_turbo232 )
 	MCFG_MOS6551_ADD(MOS6551_TAG, XTAL_3_6864MHz, DEVWRITELINE(DEVICE_SELF, c64_turbo232_cartridge_device, acia_irq_w))
+	MCFG_MOS6551_RXD_TXD_CALLBACKS(NULL, DEVWRITELINE(RS232_TAG, rs232_port_device, tx))
 
 	MCFG_RS232_PORT_ADD(RS232_TAG, rs232_intf, rs232_devices, NULL, NULL)
 MACHINE_CONFIG_END