log this write for further research

src/mame/tvgames/xavix.cpp

@@ -432,7 +432,7 @@ void xavix_state::superxavix_lowbus_map(address_map &map)
 	// map(0x6a40, 0x6a7f).ram().share("ext_segment_regs"); // 16x32 extended segment regs
 
 	 // bitmap plotter(!) (with auto-inc?) - used by super pc tv units
-	map(0x6f60, 0x6f60).nopw(); // writes here to flush plotter FIFO
+	map(0x6f60, 0x6f60).w(FUNC(xavix_state::superxavix_plt_flush_w)); // writes here to flush plotter FIFO
 	map(0x6f62, 0x6f62).w(FUNC(xavix_state::superxavix_plt_dat_w)); // writes plotter data here
 	// 0x6f63 can be used to read from bitmap?
 	map(0x6f64, 0x6f67).rw(FUNC(xavix_state::superxavix_plt_loc_r), FUNC(xavix_state::superxavix_plt_loc_w)).share("sx_plt_loc");

src/mame/tvgames/xavix.h

@@ -441,6 +441,7 @@ class xavix_state : public driver_device
 	void superxavix_crtc_2_w(offs_t offset, uint8_t data);
 	uint8_t superxavix_crtc_2_r(offs_t offset);
 
+	void superxavix_plt_flush_w(uint8_t data);
 	void superxavix_plt_dat_w(uint8_t data);
 	void superxavix_plt_loc_w(offs_t offset, uint8_t data);
 	uint8_t superxavix_plt_loc_r(offs_t offset);
@@ -562,6 +563,7 @@ class xavix_state : public driver_device
 	uint8_t m_superxavix_pal_index = 0;
 	uint8_t m_superxavix_bitmap_pal_index = 0;
 	uint32_t m_sx_plt_address = 0;
+	uint8_t m_sx_plt_mode = 0;
 
 	int16_t get_vectors(int which, int half);
 

src/mame/tvgames/xavix_m.cpp

@@ -902,6 +902,7 @@ void xavix_state::machine_start()
 	save_item(NAME(m_superxavix_pal_index));
 	save_item(NAME(m_superxavix_bitmap_pal_index));
 	save_item(NAME(m_sx_plt_address));
+	save_item(NAME(m_sx_plt_mode));
 
 	save_item(NAME(m_sx_extended_extbus));
 }

src/mame/tvgames/xavix_v.cpp

@@ -133,10 +133,21 @@ uint8_t xavix_state::superxavix_crtc_2_r(offs_t offset)
 	return m_sx_crtc_2[offset];
 }
 
+void xavix_state::superxavix_plt_flush_w(uint8_t data)
+{
+	// flush current write buffer, maybe also set write mode?
+	logerror("%s: superxavix_plt_flush_w %02x\n", machine().describe_context(), data);
+	m_sx_plt_mode = data;
+}
+
+
 void xavix_state::superxavix_plt_dat_w(uint8_t data)
 {
-	uint32_t realaddress = m_sx_plt_address / 0x8;
+	uint32_t realaddress = m_sx_plt_address / 0x8; // it's a bit-offset?
+
+	//if (m_sx_plt_mode == 0x07) // maybe 8bpp, suprtvpc doesn't write the bad status bar or bad text with this, but suprtvpchk drawing breaks
 	m_maincpu->space(6).write_byte(realaddress & 0x7fffff, data);
+
 	m_sx_plt_address += 0x8;
 }