From c6ee172dbec6021ae6a42e3e7372b8895745b1be Mon Sep 17 00:00:00 2001
From: AJR <ajrhacker@users.noreply.github.com>
Date: Fri, 24 Apr 2020 11:16:14 -0400
Subject: [PATCH] 6883sam: Another blind attempt at fixing 64K mode (nw)

---
 src/mame/drivers/coco12.cpp  |  4 ++--
 src/mame/machine/6883sam.cpp | 10 +++++++---
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/mame/drivers/coco12.cpp b/src/mame/drivers/coco12.cpp
index ccabd545750..d95ae5a5fea 100644
--- a/src/mame/drivers/coco12.cpp
+++ b/src/mame/drivers/coco12.cpp
@@ -66,13 +66,13 @@ void coco12_state::coco_ram(address_map &map)
 void coco12_state::coco_rom0(address_map &map)
 {
 	// $8000-$9FFF
-	map(0x0000, 0x1fff).rom().region(MAINCPU_TAG, 0x0000);
+	map(0x0000, 0x1fff).rom().region(MAINCPU_TAG, 0x0000).nopw();
 }
 
 void coco12_state::coco_rom1(address_map &map)
 {
 	// $A000-$BFFF
-	map(0x0000, 0x1fff).rom().region(MAINCPU_TAG, 0x2000);
+	map(0x0000, 0x1fff).rom().region(MAINCPU_TAG, 0x2000).nopw();
 }
 
 void coco12_state::coco_rom2(address_map &map)
diff --git a/src/mame/machine/6883sam.cpp b/src/mame/machine/6883sam.cpp
index 89a9a3bf7af..8209d479dd1 100644
--- a/src/mame/machine/6883sam.cpp
+++ b/src/mame/machine/6883sam.cpp
@@ -162,7 +162,7 @@ uint8_t sam6883_device::read(offs_t offset)
 	}
 	else if (offset < 0xff00)
 	{
-		// ROM2 space: C000–DFFF
+		// ROM2 space: C000–FEFF
 		return m_rom_space[2]->read_byte(offset & 0x3fff);
 	}
 	else if (offset < 0xff60)
@@ -184,10 +184,10 @@ uint8_t sam6883_device::read(offs_t offset)
 
 void sam6883_device::write(offs_t offset, uint8_t data)
 {
+	bool mode_64k = (m_sam_state & SAM_STATE_M1) == SAM_STATE_M1;
 	if (offset < 0x8000)
 	{
 		// RAM write space: 0000–7FFF (nominally space 7)
-		bool mode_64k = (m_sam_state & SAM_STATE_M1) == SAM_STATE_M1;
 		if (mode_64k && (m_sam_state & (SAM_STATE_TY|SAM_STATE_P1)) == SAM_STATE_P1)
 			offset |= 0x8000;
 		m_ram_space->write_byte(offset, data);
@@ -195,11 +195,15 @@ void sam6883_device::write(offs_t offset, uint8_t data)
 	else if (offset < 0xc000 || offset >= 0xffe0)
 	{
 		// ROM spaces: 8000–9FFF and A000–BFFF + FFE0–FFFF (may write through to RAM)
+		if (offset < 0xc000 && mode_64k && (m_sam_state & SAM_STATE_TY))
+			m_ram_space->write_byte(offset, data);
 		m_rom_space[BIT(offset, 13)]->write_byte(offset & 0x1fff, data);
 	}
 	else if (offset < 0xff00)
 	{
-		// ROM2 space: C000–DFFF (may write through to RAM)
+		// ROM2 space: C000–FEFF (may write through to RAM)
+		if (mode_64k && (m_sam_state & SAM_STATE_TY))
+			m_ram_space->write_byte(offset, data);
 		m_rom_space[2]->write_byte(offset & 0x3fff, data);
 	}
 	else if (offset < 0xff60)