diff --git a/c64/basic/a533.linkprg.s b/c64/basic/a533.linkprg.s
index 57d6bdda..859faa8a 100644
--- a/c64/basic/a533.linkprg.s
+++ b/c64/basic/a533.linkprg.s
@@ -34,7 +34,10 @@ linkprg_loop:
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
 	cmp #$00
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
@@ -54,7 +57,9 @@ linkprg_end_of_line_search:
 #elif CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
diff --git a/c64/basic/basic_commands/cmd_list.s b/c64/basic/basic_commands/cmd_list.s
index 93a1fdf3..be79ad4c 100644
--- a/c64/basic/basic_commands/cmd_list.s
+++ b/c64/basic/basic_commands/cmd_list.s
@@ -19,6 +19,9 @@ list_loop:
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
 	cmp #$00
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/basic_commands/cmd_print.s b/c64/basic/basic_commands/cmd_print.s
index 29ded5de..66443f4c 100644
--- a/c64/basic/basic_commands/cmd_print.s
+++ b/c64/basic/basic_commands/cmd_print.s
@@ -47,6 +47,10 @@ cmd_print_string:
 	ldx #<(__FAC1 + 1)
 	jsr peek_under_roms
 
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+	jsr peek_under_roms_via_FAC1_PLUS_1
+
 #else // CONFIG_MEMORY_MODEL_38K
 
 	lda (__FAC1 + 1), y
diff --git a/c64/basic/basic_delete_line.s b/c64/basic/basic_delete_line.s
index d7491d1d..864fd0c7 100644
--- a/c64/basic/basic_delete_line.s
+++ b/c64/basic/basic_delete_line.s
@@ -23,6 +23,8 @@ basic_delete_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -32,6 +34,8 @@ basic_delete_line:
 
 #if CONFIG_MEMORY_MODEL_60K	
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/basic_do_new.s b/c64/basic/basic_do_new.s
index aae36217..0c9119eb 100644
--- a/c64/basic/basic_do_new.s
+++ b/c64/basic/basic_do_new.s
@@ -53,22 +53,27 @@ basic_do_clr:
 	beq !+
 #if CONFIG_MEMORY_MODEL_60K
 	lda #>$F7FF
+#elif CONFIG_MEMORY_MODEL_50K
+	lda #>$D000	
+#elif CONFIG_MEMORY_MODEL_46K
+	lda #>$C000
 #else // CONFIG_MEMORY_MODEL_38K
 	lda #>$A000
 #endif
-	.byte $2C
+	skip_2_bytes_trash_nvz
 !:	
-#if CONFIG_MEMORY_MODEL_60K
-	lda #>$F7FF
-#else // CONFIG_MEMORY_MODEL_38K
-	lda #>$A000
-#endif
+	lda #>$8000
 	sta MEMSIZ+1
 	sta FRETOP+1
 #if CONFIG_MEMORY_MODEL_60K
-	lda #<$F7FF
-#else // CONFIG_MEMORY_MODEL_38K
-	lda #<$A000
+	cpx #$80
+	beq !+
+	lda #$FF
+	skip_2_bytes_trash_nvz
+!:
+	lda #<$00
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	lda #<$00
 #endif
 	sta MEMSIZ+0
 	sta FRETOP+0
diff --git a/c64/basic/basic_find_line.s b/c64/basic/basic_find_line.s
index 45102507..be9a962e 100644
--- a/c64/basic/basic_find_line.s
+++ b/c64/basic/basic_find_line.s
@@ -22,6 +22,8 @@ basic_find_line_loop:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -36,6 +38,8 @@ basic_find_line_loop:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -66,6 +70,8 @@ more_lines_exist:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -75,6 +81,8 @@ more_lines_exist:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/basic_find_next_line.s b/c64/basic/basic_find_next_line.s
index 6c2cba88..cd38025f 100644
--- a/c64/basic/basic_find_next_line.s
+++ b/c64/basic/basic_find_next_line.s
@@ -12,6 +12,8 @@ basic_find_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -21,6 +23,8 @@ basic_find_next_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/basic_follow_link_to_next_line.s b/c64/basic/basic_follow_link_to_next_line.s
index 5a4acd2c..b0b4e57a 100644
--- a/c64/basic/basic_follow_link_to_next_line.s
+++ b/c64/basic/basic_follow_link_to_next_line.s
@@ -8,6 +8,8 @@ basic_follow_link_to_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -17,6 +19,8 @@ basic_follow_link_to_next_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/basic_insert_line.s b/c64/basic/basic_insert_line.s
index 25212e01..7aff08ab 100644
--- a/c64/basic/basic_insert_line.s
+++ b/c64/basic/basic_insert_line.s
@@ -67,7 +67,7 @@ basic_insert_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
@@ -76,7 +76,7 @@ basic_insert_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
@@ -91,7 +91,7 @@ line_store_loop:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
diff --git a/c64/basic/basic_shift_mem_down.s b/c64/basic/basic_shift_mem_down.s
index 0ab14abd..30216b77 100644
--- a/c64/basic/basic_shift_mem_down.s
+++ b/c64/basic/basic_shift_mem_down.s
@@ -3,6 +3,9 @@
 // #LAYOUT# *   *       #IGNORE
 
 
+// XXX review this code - for memory models below 60k this can probably be simplified
+
+
 basic_shift_mem_down_and_relink:
 	// Shift memory down to basic_current_line_pointer
 	// from X bytes further along.
@@ -123,6 +126,8 @@ relink_down_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -134,6 +139,8 @@ relink_down_next_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -147,7 +154,7 @@ relink_down_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
@@ -156,7 +163,7 @@ relink_down_next_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
diff --git a/c64/basic/basic_shift_mem_up.s b/c64/basic/basic_shift_mem_up.s
index 3ff1eb07..d4cdad86 100644
--- a/c64/basic/basic_shift_mem_up.s
+++ b/c64/basic/basic_shift_mem_up.s
@@ -3,6 +3,9 @@
 // #LAYOUT# *   *       #IGNORE
 
 
+// XXX review this code - for memory models below 60k this can probably be simplified
+
+
 basic_shift_mem_up_and_relink:
 	// Shift memory up from OLDTXT
 	// X bytes.
@@ -114,7 +117,7 @@ basic_shift_mem_up_and_relink:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr poke_under_roms
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 
@@ -137,6 +140,8 @@ relink_up_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -151,6 +156,8 @@ relink_up_next_line:
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
 	cmp #$00
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/board_m65/mega65_imports.s b/c64/basic/board_m65/mega65_imports.s
index de496d3b..3cf9df91 100644
--- a/c64/basic/board_m65/mega65_imports.s
+++ b/c64/basic/board_m65/mega65_imports.s
@@ -18,9 +18,6 @@
 .label print_integer                   = BASIC_0.proxy_B1_print_integer
 .label print_return                    = BASIC_0.proxy_B1_print_return
 .label print_space                     = BASIC_0.proxy_B1_print_space
-#if CONFIG_SHOW_PAL_NTSC
-.label print_pal_ntsc                  = BASIC_0.proxy_B1_print_pal_ntsc
-#endif
 #if CONFIG_SHOW_FEATURES
 .label print_features                  = BASIC_0.proxy_B1_print_features
 #endif
diff --git a/c64/basic/board_m65/mega65_proxies.s b/c64/basic/board_m65/mega65_proxies.s
index 91808310..c746d06f 100644
--- a/c64/basic/board_m65/mega65_proxies.s
+++ b/c64/basic/board_m65/mega65_proxies.s
@@ -11,6 +11,9 @@ proxy_B1_peek_via_OLDTXT:
 	jsr map_NORMAL
 #if CONFIG_MEMORY_MODEL_60K
 	.error "not implemented"
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -21,7 +24,7 @@ proxy_B1_poke_via_OLDTXT:
 	jsr map_NORMAL
 #if CONFIG_MEMORY_MODEL_60K
 	.error "not implemented"
-#else // CONFIG_MEMORY_MODEL_38K
+#else // CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 	sta (OLDTXT),y
 #endif
 	jmp map_BASIC_1
@@ -54,17 +57,6 @@ proxy_B1_print_space:
 	jsr print_space
 	jmp map_BASIC_1
 
-
-#if CONFIG_SHOW_PAL_NTSC
-
-proxy_B1_print_pal_ntsc:
-
-	jsr map_NORMAL
-	jsr print_pal_ntsc
-	jmp map_BASIC_1
-
-#endif
-
 #if CONFIG_SHOW_FEATURES
 
 proxy_B1_print_features:
diff --git a/c64/basic/e000.under_rom_routines_46k_50k.s b/c64/basic/e000.under_rom_routines_46k_50k.s
new file mode 100644
index 00000000..771b5dc2
--- /dev/null
+++ b/c64/basic/e000.under_rom_routines_46k_50k.s
@@ -0,0 +1,72 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// XXX extend build_segment tool to allow to specify placement range
+
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+
+peek_under_roms_via_TXTPTR:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Retrieve value from under ROMs
+
+	lda (TXTPTR), y
+
+	// FALLTROUGH
+
+peek_under_roms_finalize:
+
+	// Restore memory mapping
+
+	pha
+	lda #$27
+	sta CPU_R6510
+	pla
+
+	// Quit
+
+	rts
+
+peek_under_roms_via_OLDTXT:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Retrieve value from under ROMs
+
+	lda (TXTPTR), y
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+peek_under_roms_via_FAC1_PLUS_1:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Retrieve value from under ROMs
+
+	lda (__FAC1 + 1), y
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+
+#endif
diff --git a/c64/basic/engine/end_of_statement_check.s b/c64/basic/engine/end_of_statement_check.s
index 16ff1371..2c7a7271 100644
--- a/c64/basic/engine/end_of_statement_check.s
+++ b/c64/basic/engine/end_of_statement_check.s
@@ -16,6 +16,8 @@ end_of_statement_check:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<TXTPTR
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_TXTPTR
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (TXTPTR),y
 #endif
diff --git a/c64/basic/engine/execute_line_statements.s b/c64/basic/engine/execute_line_statements.s
index 6b85037b..58b10a3d 100644
--- a/c64/basic/engine/execute_line_statements.s
+++ b/c64/basic/engine/execute_line_statements.s
@@ -208,6 +208,8 @@ execute_line:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -217,6 +219,8 @@ execute_line:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/engine/fetch_character.s b/c64/basic/engine/fetch_character.s
index ddef18b5..68397cc7 100644
--- a/c64/basic/engine/fetch_character.s
+++ b/c64/basic/engine/fetch_character.s
@@ -16,6 +16,10 @@ fetch_character:
 	ldx #<TXTPTR
 	jsr peek_under_roms
 
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+	jsr peek_under_roms_via_TXTPTR
+
 #else // CONFIG_MEMORY_MODEL_38K
 
 	lda (TXTPTR),y
diff --git a/c64/basic/peek_line_pointer_null_check.s b/c64/basic/peek_line_pointer_null_check.s
index d3368be5..a73351d4 100644
--- a/c64/basic/peek_line_pointer_null_check.s
+++ b/c64/basic/peek_line_pointer_null_check.s
@@ -13,6 +13,9 @@ peek_line_pointer_null_check:
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
 	cmp #$00
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -23,6 +26,9 @@ peek_line_pointer_null_check:
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
 	cmp #$00
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
diff --git a/c64/basic/print/list_single_line.s b/c64/basic/print/list_single_line.s
index 7a3e5a35..a97077b5 100644
--- a/c64/basic/print/list_single_line.s
+++ b/c64/basic/print/list_single_line.s
@@ -21,7 +21,9 @@ list_single_line:
 	jsr peek_via_OLDTXT
 #elif CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
@@ -32,7 +34,9 @@ list_single_line:
 	jsr peek_via_OLDTXT
 #elif CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
@@ -56,7 +60,10 @@ list_print_loop:
 	ldx #<OLDTXT
 	jsr peek_under_roms
 	cmp #$00
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
@@ -96,7 +103,10 @@ list_display_token_CC:
 	ldx #<OLDTXT
 	jsr peek_under_roms
 	cmp #$00
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
@@ -131,7 +141,10 @@ list_display_token_CD:
 	ldx #<OLDTXT
 	jsr peek_under_roms
 	cmp #$00
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_via_OLDTXT
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 	
diff --git a/c64/basic/under_rom_routines.s b/c64/basic/under_rom_routines_60k.s
similarity index 97%
rename from c64/basic/under_rom_routines.s
rename to c64/basic/under_rom_routines_60k.s
index 611b7e65..e4458496 100644
--- a/c64/basic/under_rom_routines.s
+++ b/c64/basic/under_rom_routines_60k.s
@@ -2,14 +2,14 @@
 // #LAYOUT# *   BASIC_0 #TAKE
 // #LAYOUT# *   *       #IGNORE
 
-// IMPORTANT:
-// These routines lengths cannot be changed without changing
-// the aliases for peek_under_roms, poke_under_roms etc
-// in ,aliases.s.
-// Thus those addresses are expressed using formulae.
 
 #if CONFIG_MEMORY_MODEL_60K
 
+// IMPORTANT:
+// These routines lengths cannot be changed without changing
+// the aliases for peek_under_roms, poke_under_roms, etc.
+// Thus those addresses are expressed using formulae.
+
 install_ram_routines:
 	// Copy routines into place
 	ldx #__ram_routines_end-__ram_routines_start-1
diff --git a/c64/kernal/iec/iec_send_file_name.s b/c64/kernal/iec/iec_send_file_name.s
index 8d61cb20..2c850cf9 100644
--- a/c64/kernal/iec/iec_send_file_name.s
+++ b/c64/kernal/iec/iec_send_file_name.s
@@ -21,7 +21,7 @@ iec_send_file_name_loop:
 	ldx #<FNADDR+0
 	jsr peek_under_roms
 #elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_FNADDR
+	jsr peek_under_roms_via_FNADDR
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (FNADDR),y
 #endif
diff --git a/c64/kernal/iec/save_iec.s b/c64/kernal/iec/save_iec.s
index 80e3f8c0..262789ca 100644
--- a/c64/kernal/iec/save_iec.s
+++ b/c64/kernal/iec/save_iec.s
@@ -83,7 +83,7 @@ iec_save_loop:
 	ldx #<MEMUSS+0
 	jsr peek_under_roms
 #elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_MEMUSS
+	jsr peek_under_roms_via_MEMUSS
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (MEMUSS),y
 #endif
diff --git a/c64/kernal/iostack/load_save_common.s b/c64/kernal/iostack/load_save_common.s
index 7e1b7503..6c5dc73e 100644
--- a/c64/kernal/iostack/load_save_common.s
+++ b/c64/kernal/iostack/load_save_common.s
@@ -68,8 +68,14 @@ lvs_handle_byte_verify:
 
 #elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
 
+	// Store byte for comparing
+	sta TBTCNT
+
 	ldy #0
-	jsr peek_under_roms_EAL
+	jsr peek_under_roms_via_EAL
+
+	// Compare with stored byte
+	cmp TBTCNT
 
 #else // CONFIG_MEMORY_MODEL_38K
 
@@ -140,7 +146,7 @@ lvs_display_searching_for:
 	ldx #<FNADDR+0
 	jsr peek_under_roms
 #elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_FNADDR
+	jsr peek_under_roms_via_FNADDR
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (FNADDR),y
 #endif
diff --git a/c64/kernal/memory/under_rom_routines_46k_50k.s b/c64/kernal/memory/under_rom_routines_46k_50k.s
new file mode 100644
index 00000000..0db1dc6b
--- /dev/null
+++ b/c64/kernal/memory/under_rom_routines_46k_50k.s
@@ -0,0 +1,85 @@
+// #LAYOUT# STD *        #TAKE
+// #LAYOUT# *   KERNAL_0 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+
+#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
+
+
+peek_under_roms_via_MEMUSS:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (MEMUSS), y
+
+	// FALLTROUGH
+
+peek_under_roms_finalize:
+
+	// Store value in a safe place
+
+	tax
+
+	// Restore memory mapping
+
+	pla
+	sta CPU_R6510
+
+	// Retrieve value and quit
+
+	txa
+	rts
+
+
+peek_under_roms_via_FNADDR:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (FNADDR), y
+
+	// Continue using common code
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+
+peek_under_roms_via_EAL:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (EAL), y
+
+	// Continue using common code
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+
+#endif
diff --git a/c64/kernal/memory/under_rom_routines.s b/c64/kernal/memory/under_rom_routines_60k.s
similarity index 52%
rename from c64/kernal/memory/under_rom_routines.s
rename to c64/kernal/memory/under_rom_routines_60k.s
index c43d908a..2dc64876 100644
--- a/c64/kernal/memory/under_rom_routines.s
+++ b/c64/kernal/memory/under_rom_routines_60k.s
@@ -3,86 +3,7 @@
 // #LAYOUT# *   *        #IGNORE
 
 
-#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
-
-
-peek_under_roms_MEMUSS:
-
-	// Store current memory mapping, unmap BASIC ROM
-
-	lda CPU_R6510
-	pha
-	and #$FE
-	sta CPU_R6510 
-
-	// Retrieve value from under ROMs
-
-	lda (MEMUSS), y
-
-	// FALLTROUGH
-
-peek_under_roms_finalize:
-
-	// Store value in a safe place
-
-	tax
-
-	// Restore memory mapping
-
-	pla
-	sta CPU_R6510
-
-	// Retrieve value and quit
-
-	txa
-	rts
-
-
-peek_under_roms_FNADDR:
-
-	// Store current memory mapping, unmap BASIC ROM
-
-	lda CPU_R6510
-	pha
-	and #$FE
-	sta CPU_R6510 
-
-	// Retrieve value from under ROMs
-
-	lda (FNADDR), y
-
-	// Continue using common code
-
-#if HAS_OPCODES_65C02
-	bra peek_under_roms_finalize
-#else
-	jmp peek_under_roms_finalize
-#endif
-
-
-peek_under_roms_EAL:
-
-	// Store current memory mapping, unmap BASIC ROM
-
-	lda CPU_R6510
-	pha
-	and #$FE
-	sta CPU_R6510 
-
-	// Retrieve value from under ROMs
-
-	lda (EAL), y
-
-	// Continue using common code
-
-#if HAS_OPCODES_65C02
-	bra peek_under_roms_finalize
-#else
-	jmp peek_under_roms_finalize
-#endif
-
-
-#elif CONFIG_MEMORY_MODEL_60K
+#if CONFIG_MEMORY_MODEL_60K
 
 
 // IMPORTANT:
diff --git a/c64/kernal/rs232/close_rs232.s b/c64/kernal/rs232/close_rs232.s
index d2f73820..7a254c8d 100644
--- a/c64/kernal/rs232/close_rs232.s
+++ b/c64/kernal/rs232/close_rs232.s
@@ -14,10 +14,6 @@
 	.error "CONFIG_MEMORY_MODEL_60K is not compatible with RS-232 memory allocation code"
 #endif
 
-#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
-	.error "TODO: add compatibility with these memory models"
-#endif
-
 
 close_rs232:
 
diff --git a/c64/kernal/rs232/open_rs232.s b/c64/kernal/rs232/open_rs232.s
index fc9a1c7c..06c08e65 100644
--- a/c64/kernal/rs232/open_rs232.s
+++ b/c64/kernal/rs232/open_rs232.s
@@ -14,9 +14,6 @@
 	.error "CONFIG_MEMORY_MODEL_60K is not compatible with RS-232 memory allocation code"
 #endif
 
-#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
-	.error "TODO: add compatibility with these memory models"
-#endif
 
 open_rs232: