From d2c4286eca573ed6143b50cb4acd0c8ab72db9f1 Mon Sep 17 00:00:00 2001
From: hap <happppp@users.noreply.github.com>
Date: Tue, 5 Dec 2023 20:34:30 +0100
Subject: [PATCH] m6801: mask unused ram ctrl reg bits

---
 src/devices/cpu/m6800/m6801.cpp | 15 ++++++++++++++-
 src/devices/cpu/m6800/m6801.h   |  4 +++-
 src/mame/chess/yeno_301xl.cpp   |  2 ++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/devices/cpu/m6800/m6801.cpp b/src/devices/cpu/m6800/m6801.cpp
index 1485e7f2d67..db770b8e7d8 100644
--- a/src/devices/cpu/m6800/m6801.cpp
+++ b/src/devices/cpu/m6800/m6801.cpp
@@ -1285,7 +1285,7 @@ void m6801_cpu_device::device_reset()
 	OCD = 0xffff;
 	TOD = 0xffff;
 	m_timer_next = 0xffff;
-	m_ram_ctrl |= 0x78;
+	m_ram_ctrl |= 0x40;
 	m_latch09 = 0;
 
 	m_trcsr = M6801_TRCSR_TDRE;
@@ -1311,6 +1311,7 @@ void hd6301x_cpu_device::device_reset()
 	m_tcsr2 = 0x00;
 	m_pending_tcsr2 = 0x00;
 	OC2D = 0xffff;
+	m_ram_ctrl = (m_ram_ctrl & 0x80) | 0x7c;
 
 	m_t2cnt = 0x00;
 	m_tconr = 0xff;
@@ -1333,6 +1334,7 @@ void hd6301y_cpu_device::device_reset()
 {
 	hd6301x_cpu_device::device_reset();
 
+	m_ram_ctrl = (m_ram_ctrl & 0x80) | 0x78;
 	m_p6csr = 7;
 }
 
@@ -2231,6 +2233,17 @@ void m6801_cpu_device::sci_tdr_w(uint8_t data)
 
 uint8_t m6801_cpu_device::rcr_r()
 {
+	return m_ram_ctrl | 0x3f;
+}
+
+uint8_t hd6301x_cpu_device::rcr_r()
+{
+	return m_ram_ctrl | 0x30;
+}
+
+uint8_t hd6301y_cpu_device::rcr_r()
+{
+	// no unused bits
 	return m_ram_ctrl;
 }
 
diff --git a/src/devices/cpu/m6800/m6801.h b/src/devices/cpu/m6800/m6801.h
index 89d9d609409..499aae2dc6f 100644
--- a/src/devices/cpu/m6800/m6801.h
+++ b/src/devices/cpu/m6800/m6801.h
@@ -122,7 +122,7 @@ protected:
 	uint8_t sci_rdr_r();
 	void sci_tdr_w(uint8_t data);
 
-	uint8_t rcr_r();
+	virtual uint8_t rcr_r();
 	virtual void rcr_w(uint8_t data);
 	uint8_t ff_r();
 
@@ -340,6 +340,7 @@ protected:
 	virtual void p6_data_w(uint8_t data);
 	uint8_t p7_data_r();
 	void p7_data_w(uint8_t data);
+	virtual uint8_t rcr_r() override;
 
 	uint8_t tcsr2_r();
 	void tcsr2_w(uint8_t data);
@@ -442,6 +443,7 @@ protected:
 	virtual void p6_data_w(uint8_t data) override;
 	uint8_t p6_csr_r();
 	void p6_csr_w(uint8_t data);
+	virtual uint8_t rcr_r() override;
 	virtual void rcr_w(uint8_t data) override;
 
 	virtual void m6800_check_irq2() override;
diff --git a/src/mame/chess/yeno_301xl.cpp b/src/mame/chess/yeno_301xl.cpp
index 8e641158a89..32e8cb458a1 100644
--- a/src/mame/chess/yeno_301xl.cpp
+++ b/src/mame/chess/yeno_301xl.cpp
@@ -16,6 +16,8 @@ Hardware notes:
 - Hitachi HD63B01X0, 8MHz XTAL
 - 8*8 chessboard buttons, 16+1 LEDs, piezo
 
+Yeno 309 XT is on the same PCB, and has the same MCU ROM.
+
 TODO:
 - if/when MAME supports an exit callback, hook up power-off IRQ to that