From 12505514eccac9b4f5ed59a7466f408314f0f90f Mon Sep 17 00:00:00 2001
From: cracyc <cracyc@users.noreply.github.com>
Date: Mon, 29 Jun 2015 17:57:57 -0500
Subject: [PATCH] m20: fix 2.0 bioses booting, requires image with nonempty
 first sector (nw)

---
 src/mess/drivers/m20.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/mess/drivers/m20.c b/src/mess/drivers/m20.c
index b5de310407e..652a1b77bbd 100644
--- a/src/mess/drivers/m20.c
+++ b/src/mess/drivers/m20.c
@@ -755,6 +755,9 @@ void m20_state::machine_reset()
 	else
 		m_port21 = 0xff;
 
+	if(system_bios() > 0)  // bits have different meanings?
+		m_port21 &= ~8;
+
 	m_fd1797->reset();
 
 	memcpy(RAM, ROM, 8);  // we need only the reset vector