diff --git a/src/emu/bus/ecbbus/grip.c b/src/emu/bus/ecbbus/grip.c
index 6c75abb49bb..4a5d54e2cc4 100644
--- a/src/emu/bus/ecbbus/grip.c
+++ b/src/emu/bus/ecbbus/grip.c
@@ -477,7 +477,6 @@ static Z80STI_INTERFACE( sti_intf )
 	DEVCB_CPU_INPUT_LINE(Z80_TAG, INPUT_LINE_IRQ0),         // interrupt
 	DEVCB_DEVICE_MEMBER(DEVICE_SELF_OWNER, grip_device, sti_gpio_r),    // GPIO read
 	DEVCB_NULL,                                             // GPIO write
-	DEVCB_NULL,                                             // serial input
 	DEVCB_NULL,                                             // serial output
 	DEVCB_NULL,                                             // timer A output
 	DEVCB_DEVICE_LINE_MEMBER(DEVICE_SELF_OWNER, grip_device, speaker_w),    // timer B output
diff --git a/src/emu/machine/z80sti.c b/src/emu/machine/z80sti.c
index d8b47d64a8d..e6d0742d6c3 100644
--- a/src/emu/machine/z80sti.c
+++ b/src/emu/machine/z80sti.c
@@ -123,7 +123,6 @@ void z80sti_device::device_config_complete()
 		memset(&m_out_int_cb, 0, sizeof(m_out_int_cb));
 		memset(&m_in_gpio_cb, 0, sizeof(m_in_gpio_cb));
 		memset(&m_out_gpio_cb, 0, sizeof(m_out_gpio_cb));
-		memset(&m_in_si_cb, 0, sizeof(m_in_si_cb));
 		memset(&m_out_so_cb, 0, sizeof(m_out_so_cb));
 		memset(&m_out_tao_cb, 0, sizeof(m_out_tao_cb));
 		memset(&m_out_tbo_cb, 0, sizeof(m_out_tbo_cb));
@@ -142,7 +141,6 @@ void z80sti_device::device_start()
 	// resolve callbacks
 	m_in_gpio_func.resolve(m_in_gpio_cb, *this);
 	m_out_gpio_func.resolve(m_out_gpio_cb, *this);
-	m_in_si_func.resolve(m_in_si_cb, *this);
 	m_out_so_func.resolve(m_out_so_cb, *this);
 	m_out_timer_func[TIMER_A].resolve(m_out_tao_cb, *this);
 	m_out_timer_func[TIMER_B].resolve(m_out_tbo_cb, *this);
diff --git a/src/emu/machine/z80sti.h b/src/emu/machine/z80sti.h
index 84fe983bf5d..d3d522fa23f 100644
--- a/src/emu/machine/z80sti.h
+++ b/src/emu/machine/z80sti.h
@@ -71,9 +71,6 @@ struct z80sti_interface
 	// this is called on each write of the GPIO pins
 	devcb_write8            m_out_gpio_cb;
 
-	// this gets called for each read of the SI pin (pin 38)
-	devcb_read_line         m_in_si_cb;
-
 	// this gets called for each change of the SO pin (pin 37)
 	devcb_write_line        m_out_so_cb;