diff --git a/src/emu/bus/epson_sio/tf20.c b/src/emu/bus/epson_sio/tf20.c
index 47422e0f31e..ac213e34934 100644
--- a/src/emu/bus/epson_sio/tf20.c
+++ b/src/emu/bus/epson_sio/tf20.c
@@ -289,7 +289,7 @@ WRITE8_MEMBER( epson_tf20_device::fdc_control_w )
 WRITE_LINE_MEMBER( epson_tf20_device::rxc_w )
 {
 	m_rxc = state;
-	m_sio_input->rx_w(m_txda & m_rxc);
+	m_sio_input->rx_w(m_txda && m_rxc);
 }
 
 //-------------------------------------------------
@@ -299,7 +299,7 @@ WRITE_LINE_MEMBER( epson_tf20_device::rxc_w )
 WRITE_LINE_MEMBER( epson_tf20_device::pinc_w )
 {
 	m_pinc = state;
-	m_sio_input->pin_w(!m_dtra | m_pinc);
+	m_sio_input->pin_w(!m_dtra || m_pinc);
 }
 
 //-------------------------------------------------
@@ -309,7 +309,7 @@ WRITE_LINE_MEMBER( epson_tf20_device::pinc_w )
 WRITE_LINE_MEMBER( epson_tf20_device::txda_w )
 {
 	m_txda = state;
-	m_sio_input->rx_w(m_txda & m_rxc);
+	m_sio_input->rx_w(m_txda && m_rxc);
 }
 
 //-------------------------------------------------
@@ -319,7 +319,7 @@ WRITE_LINE_MEMBER( epson_tf20_device::txda_w )
 WRITE_LINE_MEMBER( epson_tf20_device::dtra_w )
 {
 	m_dtra = state;
-	m_sio_input->pin_w(!m_dtra | m_pinc);
+	m_sio_input->pin_w(!m_dtra || m_pinc);
 }
 
 //-------------------------------------------------
diff --git a/src/mess/drivers/altos5.c b/src/mess/drivers/altos5.c
index c9155cac15f..acd440b2cdb 100644
--- a/src/mess/drivers/altos5.c
+++ b/src/mess/drivers/altos5.c
@@ -119,11 +119,11 @@ UINT8 altos5_state::convert(offs_t offset, bool state)
 	UINT8 data = m_p_prom[offset];
 
 	// if IPL and /A12, point at rom
-	if (!state & m_ipl & !BIT(offset, 0))
+	if (!state && m_ipl && !BIT(offset, 0))
 		data = 0x31;
 	else
 	// if WPRT point at nothing
-	if (state & BIT(data, 7))
+	if (state && BIT(data, 7))
 		data = 0x30;
 
 	// mask off wprt (no longer needed)
diff --git a/src/mess/drivers/mkit09.c b/src/mess/drivers/mkit09.c
index 88cd45e391e..773392850aa 100644
--- a/src/mess/drivers/mkit09.c
+++ b/src/mess/drivers/mkit09.c
@@ -149,7 +149,7 @@ READ8_MEMBER( mkit09_state::pa_r )
 // read cassette
 READ8_MEMBER( mkit09_state::pb_r )
 {
-	return m_keydata | (m_cass->input() > +0.03) ? 0x80 : 0;
+	return m_keydata | ((m_cass->input() > +0.03) ? 0x80 : 0);
 }
 
 // write display segments