From 6d445048994f50afb95df749cb90a6b47920fd20 Mon Sep 17 00:00:00 2001
From: Michael Zapf <Michael.Zapf@mizapf.de>
Date: Wed, 15 May 2019 23:07:24 +0200
Subject: [PATCH] tms9901: Ensure that the INT3 input is disabled when the
 clock is enabled.

---
 src/devices/machine/tms9901.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/devices/machine/tms9901.cpp b/src/devices/machine/tms9901.cpp
index 7f85114128a..bb7148a91a6 100644
--- a/src/devices/machine/tms9901.cpp
+++ b/src/devices/machine/tms9901.cpp
@@ -188,11 +188,18 @@ void tms9901_device::prioritize_interrupts()
 	// Skip the rightmost bit
 	uint16_t masked_ints = m_int_line;
 
-	// Do we have a timer interrupt?
-	if (m_clock_register != 0 && m_timer_int_pending)
+	// Is the clock enabled?
+	if (m_clock_register != 0)
 	{
-		masked_ints |= (1<<INT3);
-		LOGMASKED(LOG_INT, "INT3 (timer) asserted\n");
+		// Disable the actual INT3* input
+		masked_ints &= ~(1<<INT3);
+
+		// Do we have a clock interrupt?
+		if (m_timer_int_pending)
+		{
+			masked_ints |= (1<<INT3);
+			LOGMASKED(LOG_INT, "INT3 (timer) asserted\n");
+		}
 	}
 
 	m_int_level = 1;