diff --git a/src/boards/resettxrom.c b/src/boards/resettxrom.c
index 910c8a2..96b3cb4 100644
--- a/src/boards/resettxrom.c
+++ b/src/boards/resettxrom.c
@@ -2,6 +2,7 @@
  *
  * Copyright notice for this file:
  *  Copyright (C) 2019 Libretro Team
+ *  Copyright (C) 2020 negativeExponent
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -27,12 +28,35 @@
 #include "mapinc.h"
 #include "mmc3.h"
 
+static uint8 submapper;
+
 static void M313CW(uint32 A, uint8 V) {
-	setchr1(A, (EXPREGS[0] << 7) | (V & 0x7F));
+	/*FCEU_printf("CHR: A:%04x V:%02x 0:%02x\n", A, V, EXPREGS[0]);*/
+	switch (submapper) {
+	case 0: V = (EXPREGS[0] << 7) | (V & 0x7F); break;
+	case 1: V = (EXPREGS[0] << 7) | (V & 0x7F); break;
+	case 2: V = (EXPREGS[0] << 8) | (V & 0xFF); break;
+	case 3: V = (EXPREGS[0] << 8) | (V & 0xFF); break;
+	case 4: V = (EXPREGS[0] << 7) | (V & 0x7F); break;
+	}
+	setchr1(A, V);
 }
 
 static void M313PW(uint32 A, uint8 V) {
-	setprg8(A, (EXPREGS[0] << 4) | (V & 0x0F));
+	/*FCEU_printf("PRG: A:%04x V:%02x 0:%02x\n", A, V, EXPREGS[0]);*/
+	switch (submapper) {
+	case 0: V = (EXPREGS[0] << 4) | (V & 0x0F); break;
+	case 1: V = (EXPREGS[0] << 5) | (V & 0x1F); break;
+	case 2: V = (EXPREGS[0] << 4) | (V & 0x0F); break;
+	case 3: V = (EXPREGS[0] << 5) | (V & 0x1F); break;
+	case 4:
+		if (EXPREGS[0] == 0)
+			V = (EXPREGS[0] << 5) | (V & 0x1F);
+		else
+			V = (EXPREGS[0] << 4) | (V & 0x0F);
+		break;
+	}
+	setprg8(A, V);
 }
 
 static void M313Reset(void) {
@@ -48,10 +72,12 @@ static void M313Power(void) {
 
 /* NES 2.0 313, UNIF BMC-RESET-TXROM */
 void BMCRESETTXROM_Init(CartInfo *info) {
-	GenMMC3_Init(info, 128, 128, 0, 0);
+	GenMMC3_Init(info, 256, 256, 8, 0);
 	cwrap = M313CW;
 	pwrap = M313PW;
+	submapper = info->submapper;
 	info->Power = M313Power;
 	info->Reset = M313Reset;
-	AddExState(EXPREGS, 1, 0, "EXPR");
+	AddExState(&EXPREGS[0], 1, 0, "EXPR");
+	AddExState(&submapper, 1, 0, "SUBM");
 }