diff --git a/makefile b/makefile
index 46905a58..e876d2f4 100644
--- a/makefile
+++ b/makefile
@@ -1587,6 +1587,11 @@ IMLAC = ${IMLACD}/imlac_sys.c ${IMLACD}/imlac_cpu.c \
 IMLAC_OPT = -I ${IMLACD} ${DISPLAY_OPT}
 
 
+STUBD = ${SIMHD}/stub
+STUB = ${STUBD}/stub_sys.c ${STUBD}/stub_cpu.c
+STUB_OPT = -I ${STUBD}
+
+
 TT2500D = ${SIMHD}/tt2500
 TT2500 = ${TT2500D}/tt2500_sys.c ${TT2500D}/tt2500_cpu.c \
 	${TT2500D}/tt2500_dpy.c ${TT2500D}/tt2500_crt.c ${TT2500D}/tt2500_tv.c \
@@ -2250,6 +2255,12 @@ ifneq (,$(call find_test,${IMLAC},imlac))
 	$@ $(call find_test,${IMLACD},imlac) ${TEST_ARG}
 endif
 
+stub : ${BIN}stub${EXE}
+
+${BIN}stub${EXE} : ${STUB} ${SIM}
+	${MKDIRBIN}
+	${CC} ${STUB} ${SIM} ${STUB_OPT} ${CC_OUTSPEC} ${LDFLAGS}
+
 tt2500 : ${BIN}tt2500${EXE}
 
 ${BIN}tt2500${EXE} : ${TT2500} ${SIM}
diff --git a/stub/readme.txt b/stub/readme.txt
new file mode 100644
index 00000000..cb4630db
--- /dev/null
+++ b/stub/readme.txt
@@ -0,0 +1,16 @@
+You fill in sim_instr do the instruction decoding and execution.
+
+sim_load will typically take some input file and put it in memory.
+
+cpu_reg should contain all machine state.
+
+parse_sym/fprint_sym is to assemble (with DEPOSIT) and disassemble (EXAMINE-M) instructions.
+
+sim_devices is an array of DEVICE * for peripherals.  Something like
+build_dev_tab will go through the array and initialize data structures
+at run time.
+
+Refer to this: https://github.com/open-simh/simh/blob/master/doc/simh.doc
+
+Make use of asynchronous events.  sim_activate posts a future event.
+The "svc" routine will be called.
diff --git a/stub/stub_cpu.c b/stub/stub_cpu.c
new file mode 100644
index 00000000..e26f5b65
--- /dev/null
+++ b/stub/stub_cpu.c
@@ -0,0 +1,121 @@
+/* stub_cpu.c: Stub CPU simulator
+
+   Copyright (c) 2020, Lars Brinkhoff
+
+   Permission is hereby granted, free of charge, to any person obtaining a
+   copy of this software and associated documentation files (the "Software"),
+   to deal in the Software without restriction, including without limitation
+   the rights to use, copy, modify, merge, publish, distribute, sublicense,
+   and/or sell copies of the Software, and to permit persons to whom the
+   Software is furnished to do so, subject to the following conditions:
+
+   The above copyright notice and this permission notice shall be included in
+   all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+   LARS BRINKHOFF BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+   Except as contained in this notice, the name of Lars Brinkhoff shall not be
+   used in advertising or otherwise to promote the sale, use or other dealings
+   in this Software without prior written authorization from Lars Brinkhoff.
+*/
+
+#include "stub_defs.h"
+
+
+/* Debug */
+#define DBG_CPU         0001
+
+/* CPU state. */
+static uint16 PC;
+
+/* Function declaration. */
+static t_stat cpu_ex (t_value *vptr, t_addr ea, UNIT *uptr, int32 sw);
+static t_stat cpu_dep (t_value val, t_addr ea, UNIT *uptr, int32 sw);
+static t_stat cpu_reset (DEVICE *dptr);
+
+static UNIT cpu_unit = { UDATA (NULL, UNIT_FIX + UNIT_BINK, 020000) };
+
+REG cpu_reg[] = {
+  { ORDATAD (PC, PC, 13, "Program Counter") },
+  { NULL }
+};
+
+static MTAB cpu_mod[] = {
+  { 0 }
+};
+
+static DEBTAB cpu_deb[] = {
+  { "CPU", DBG_CPU },
+  { NULL, 0 }
+};
+
+DEVICE cpu_dev = {
+  "CPU", &cpu_unit, cpu_reg, cpu_mod,
+  0, 8, 16, 1, 8, 16,
+  &cpu_ex, &cpu_dep, &cpu_reset,
+  NULL, NULL, NULL, NULL, DEV_DEBUG, 0, cpu_deb,
+  NULL, NULL, NULL, NULL, NULL, NULL
+};
+
+t_stat sim_instr (void)
+{
+  t_stat reason;
+
+  if ((reason = build_dev_tab ()) != SCPE_OK)
+    return reason;
+
+  for (;;) {
+    AIO_CHECK_EVENT;
+    if (sim_interval <= 0) {
+      if ((reason = sim_process_event()) != SCPE_OK)
+        return reason;
+    }
+
+    if (sim_brk_summ && sim_brk_test(PC, SWMASK('E')))
+      return STOP_IBKPT;
+
+    if (sim_step != 0) {
+      if (--sim_step == 0)
+        return SCPE_STEP;
+    }
+  }
+
+  return SCPE_OK;
+}
+
+static t_stat cpu_ex (t_value *vptr, t_addr ea, UNIT *uptr, int32 sw)
+{
+  if (vptr == NULL)
+    return SCPE_ARG;
+  if (ea >= 040000)
+    return SCPE_NXM;
+  *vptr = M[ea];
+  return SCPE_OK;
+}
+
+static t_stat cpu_dep (t_value val, t_addr ea, UNIT *uptr, int32 sw)
+{
+  if (ea >= 040000)
+    return SCPE_NXM;
+  M[ea] = val & 0177777;
+  return SCPE_OK;
+}
+
+static t_bool pc_is_a_subroutine_call (t_addr **ret_addrs)
+{
+  return FALSE;
+}
+
+static t_stat
+cpu_reset (DEVICE *dptr)
+{
+  sim_brk_types = SWMASK('D') | SWMASK('E');
+  sim_brk_dflt = SWMASK ('E');
+  sim_vm_is_subroutine_call = &pc_is_a_subroutine_call;
+  return SCPE_OK;
+}
diff --git a/stub/stub_defs.h b/stub/stub_defs.h
new file mode 100644
index 00000000..52e69f93
--- /dev/null
+++ b/stub/stub_defs.h
@@ -0,0 +1,44 @@
+/* stub_defs.h: Stub simulator definitions
+
+   Copyright (c) 2020, Lars Brinkhoff
+
+   Permission is hereby granted, free of charge, to any person obtaining a
+   copy of this software and associated documentation files (the "Software"),
+   to deal in the Software without restriction, including without limitation
+   the rights to use, copy, modify, merge, publish, distribute, sublicense,
+   and/or sell copies of the Software, and to permit persons to whom the
+   Software is furnished to do so, subject to the following conditions:
+
+   The above copyright notice and this permission notice shall be included in
+   all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+   LARS BRINKHOFF BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+   Except as contained in this notice, the name of Lars Brinkhoff shall not be
+   used in advertising or otherwise to promote the sale, use or other dealings
+   in this Software without prior written authorization from Lars Brinkhoff.
+
+   21-Apr-20    LB      New simulator.
+*/
+
+#ifndef STUB_DEFS_H_
+#define STUB_DEFS_H_  0
+
+#include "sim_defs.h"
+
+#define STOP_HALT       1
+#define STOP_IBKPT      2
+#define STOP_ACCESS     3
+
+extern t_bool build_dev_tab (void);
+
+extern REG cpu_reg[];
+extern uint16 M[];
+extern DEVICE cpu_dev;
+
+#endif /* STUB_DEFS_H_ */
diff --git a/stub/stub_sys.c b/stub/stub_sys.c
new file mode 100644
index 00000000..c499afb5
--- /dev/null
+++ b/stub/stub_sys.c
@@ -0,0 +1,69 @@
+/* stub_sys.c: Stub simulator interface
+
+   Copyright (c) 2020, Lars Brinkhoff
+
+   Permission is hereby granted, free of charge, to any person obtaining a
+   copy of this software and associated documentation files (the "Software"),
+   to deal in the Software without restriction, including without limitation
+   the rights to use, copy, modify, merge, publish, distribute, sublicense,
+   and/or sell copies of the Software, and to permit persons to whom the
+   Software is furnished to do so, subject to the following conditions:
+
+   The above copyright notice and this permission notice shall be included in
+   all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+   LARS BRINKHOFF BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+   Except as contained in this notice, the name of Lars Brinkhoff shall not be
+   used in advertising or otherwise to promote the sale, use or other dealings
+   in this Software without prior written authorization from Lars Brinkhoff.
+
+   21-Apr-20    LB      New simulator.
+*/
+
+#include "stub_defs.h"
+
+int32 sim_emax = 1;
+char sim_name[] = "Stub";
+
+uint16 M[040000];
+REG *sim_PC = &cpu_reg[0];
+
+DEVICE *sim_devices[] = {
+  &cpu_dev,
+  NULL
+};
+  
+const char *sim_stop_messages[SCPE_BASE] = {
+  "Unknown error",
+  "HALT instruction",
+  "Breakpoint",
+  "Invalid access",
+};
+
+t_stat
+sim_load (FILE *fileref, CONST char *cptr, CONST char *fnam, int flag)
+{
+  return SCPE_OK;
+}
+
+t_bool build_dev_tab (void)
+{
+  return SCPE_OK;
+}
+
+t_stat fprint_sym (FILE *of, t_addr addr, t_value *val,
+                   UNIT *uptr, int32 sw)
+{
+}
+
+t_stat parse_sym (CONST char *cptr, t_addr addr, UNIT *uptr,
+                  t_value *val, int32 sw)
+{
+  return SCPE_OK;
+}