From a246155098df168304a9826b17c91f6cf547b8d0 Mon Sep 17 00:00:00 2001
From: Michael Zapf <github@mizapf.de>
Date: Mon, 28 Sep 2020 13:09:06 +0200
Subject: [PATCH] Fixed BQ4847 to always return 0 for its register 15; required
 for proper chip detection.

---
 src/devices/machine/bq4847.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/devices/machine/bq4847.cpp b/src/devices/machine/bq4847.cpp
index 09afd9b9424..7dd9031c814 100644
--- a/src/devices/machine/bq4847.cpp
+++ b/src/devices/machine/bq4847.cpp
@@ -305,6 +305,8 @@ uint8_t bq4847_device::read(offs_t address)
 		set_register(reg_flags, 0xff, false);
 		m_interrupt_cb(intrq_r());
 	}
+	else
+		if (regnum == reg_unused) value = 0;  // Reg 15 is locked to 0 in BQ4847
 
 	LOGMASKED(LOG_REG, "Reg %d -> %02x\n", regnum, value);