diff --git a/test.c b/test.c
index c291ca1..068373b 100644
--- a/test.c
+++ b/test.c
@@ -1,13 +1,17 @@
 #include <stdio.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <string.h>
 
-uint8_t mem[0x10000];
+static uint8_t mem[0x10000];
+static uint8_t key = 0x80;
+static uint8_t last = 0x00;
 
 void prn(int c) {
   uint8_t fp;
   __asm__("movs %0, r12": "=r"(fp));
-  printf("### $%02x ###\n", c);
+  fprintf(stderr, "### $%02x ###\n", c);
+  fflush(stderr);
   __asm__("movs r12, %0":: "r"(fp));
 }
 
@@ -15,30 +19,83 @@ void cpu6502_dump(
     uint16_t pc, uint8_t a, uint8_t x, uint8_t y, uint8_t sp, uint8_t sr) {
   uint8_t fp;
   __asm__("movs %0, r12": "=r"(fp));
-  printf("*** dump *** PC=$%04x A=$%02x X=$%02x Y=$%02x SP=$%02x "
-         "NV-B_DIZC=%d%d-%d_%d%d%d%d\n",
-         pc, a, x, y, sp, (sr >> 7) & 1, (sr >> 6) & 1, (sr >> 4) & 1,
-         (sr >> 3) & 1, (sr >> 2) & 1, (sr >> 1) & 1, sr & 1);
-  fflush(stdout);
+  fprintf(stderr, "*** dump *** PC=$%04x A=$%02x X=$%02x Y=$%02x SP=$%02x "
+          "NV-B_DIZC=%d%d-%d_%d%d%d%d\n",
+          pc, a, x, y, sp, (sr >> 7) & 1, (sr >> 6) & 1, (sr >> 4) & 1,
+          (sr >> 3) & 1, (sr >> 2) & 1, (sr >> 1) & 1, sr & 1);
+  fflush(stderr);
   __asm__("movs r12, %0":: "r"(fp));
 }
 
 uint8_t cpu6502_load(uint16_t addr) {
   uint8_t fp;
+  uint8_t result = 0;
   __asm__("movs %0, r12": "=r"(fp));
-  printf("load  $%04x => $%02x\n", addr, mem[addr]);
-  fflush(stdout);
+  if (0x0400 <= addr && addr <= 0x7ff) {
+    // Fake text VRAM.
+    result = mem[addr];
+  } else if ((0x0300 <= addr && addr <= 0x03ff) ||
+             (0x0900 <= addr && addr <= 0x0fff)) {
+    // Fake memory impl to make it run on low memory chip.
+    result = last;
+  } else if (0x1000 <= addr & addr < 0xbfff) {
+    // Bus error due to minimum memory installation.
+    return 0xff;
+    fprintf(stdout, "\e[1;1Hinvalid load $%04x\n", addr);
+    fflush(stdout);
+    abort();
+  } else if (0xc000 <= addr & addr < 0xcfff) {
+    // I/O emulation.
+    if (0xc000 == addr)
+      result = key;
+    if (0xc010 == addr)
+      key &= 0x7f;
+  } else {
+    // Installed memory.
+    result = mem[addr];
+  }
+  fprintf(stderr, "load  $%04x => $%02x\n", addr, result);
+  fflush(stderr);
   __asm__("movs r12, %0":: "r"(fp));
-  return mem[addr];
+  return result;
 }
 
 void cpu6502_store(uint16_t addr, uint8_t data) {
   uint8_t fp;
   __asm__("movs %0, r12": "=r"(fp));
-  printf("store $%04x <= $%02x\n", addr, data);
-  fflush(stdout);
+  if (0x0400 <= addr && addr <= 0x7ff) {
+    // Fake text VRAM.
+    char ascii[0x40] =
+        "@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_ !\"#$%&'()*+,-./0123456789:;<=>?";
+    mem[addr] = data;
+    int y = (addr - 0x400) >> 7;
+    int x = addr & 0x7f;
+    if (x >= 0x50) {
+      x -= 0x50;
+      y += 0x10;
+    } else if (x >= 0x28) {
+      x -= 0x28;
+      y += 0x08;
+    }
+    if (y < 24)
+      printf("\e[%d;%dH%c", y + 2, x + 1, ascii[data & 0x3f]);
+  } else if ((0x0300 <= addr && addr <= 0x03ff) ||
+             (0x0900 <= addr && addr <= 0x0fff)) {
+    // Fake memory impl to make it run on low memory chip.
+    last = data;
+  } else if (0x1000 <= addr & addr < 0xcfff) {
+    // Bus error due to minimum memory installation.
+    return;
+    fprintf(stdout, "\e[1;1Hinvalid store $%04x\n", addr);
+    fflush(stdout);
+    abort();
+  } else {
+    // Installed memory.
+    mem[addr] = data;
+  }
+  fprintf(stderr, "store $%04x <= $%02x\n", addr, data);
+  fflush(stderr);
   __asm__("movs r12, %0":: "r"(fp));
-  mem[addr] = data;
 }
 
 int main(int argc, char** argv) {
@@ -47,7 +104,7 @@ int main(int argc, char** argv) {
   fread(&mem[0xd000], 1, 0x3000, fp);
   fclose(fp);
   cpu6502_reset();
-  printf("quit: $%04x\n", cpu6502_run());
+  fprintf(stderr, "quit: $%04x\n", cpu6502_run());
   return 0;
 }