diff --git a/PDP10/pdp10_defs.h b/PDP10/pdp10_defs.h
index aeb51b78..52ad9be4 100644
--- a/PDP10/pdp10_defs.h
+++ b/PDP10/pdp10_defs.h
@@ -711,6 +711,7 @@ typedef struct pdp_dib DIB;
 #define INT_V_CR        27                              /* CD20 (CD11) */
 #define INT_V_DUPRX     28                              /* DUP11 */
 #define INT_V_DUPTX     29
+#define INT_V_CH        30                              /* CH11 Chaosnet */
 
 #define INT_RP          (1u << INT_V_RP)
 #define INT_TU          (1u << INT_V_TU)
@@ -728,6 +729,7 @@ typedef struct pdp_dib DIB;
 #define INT_CR          (1u << INT_V_CD)
 #define INT_DUPRX       (1u << INT_V_DUPRX)
 #define INT_DUPTX       (1u << INT_V_DUPTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define IPL_RP          6                               /* int levels */
 #define IPL_TU          6
diff --git a/PDP10/pdp10_ksio.c b/PDP10/pdp10_ksio.c
index f5a7c74d..ad4d92b1 100644
--- a/PDP10/pdp10_ksio.c
+++ b/PDP10/pdp10_ksio.c
@@ -2009,6 +2009,8 @@ AUTO_CON auto_tab[] = {/*c  #v  am vm  fxa   fxv */
         {0000540}, {0540} },                             /* KMC11-A comm IOP-DUP ucode - fx CSR, fx VEC */
     { { "DMR" },         1,  2,  0, 0, 
         {0004000}, {0610} },                             /* DMR11 comm - fx CSR, fx VEC */
+    { { "CH" },          1,  1,  0, 0, 
+        {04140}, {0270} },                               /* CH11 - CHAOS Net - fx CSR, fx VEC */
 #else
     { { "QBA" },         1,  0,  0, 0, 
         {017500} },                                     /* doorbell - fx CSR, no VEC */
diff --git a/PDP10/pdp10_sys.c b/PDP10/pdp10_sys.c
index d82cb2b4..25f60e77 100644
--- a/PDP10/pdp10_sys.c
+++ b/PDP10/pdp10_sys.c
@@ -62,6 +62,7 @@ extern DEVICE xu_dev;
 extern DEVICE dup_dev;
 extern DEVICE kmc_dev;
 extern DEVICE dmc_dev;
+extern DEVICE ch_dev;
 extern REG cpu_reg[];
 extern a10 saved_PC;
 
@@ -99,6 +100,7 @@ DEVICE *sim_devices[] = {
     &dup_dev,
     &kmc_dev,
     &dmc_dev,
+    &ch_dev,
     NULL
     };
 
diff --git a/PDP11/pdp11_ch.c b/PDP11/pdp11_ch.c
new file mode 100644
index 00000000..d0cc7303
--- /dev/null
+++ b/PDP11/pdp11_ch.c
@@ -0,0 +1,537 @@
+/* pdp11_ch.c: CH11 Chaosnet interface.
+  ------------------------------------------------------------------------------
+
+   Copyright (c) 2018, 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
+   THE AUTHOR 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 the author shall not be
+   used in advertising or otherwise to promote the sale, use or other dealings
+   in this Software without prior written authorization from the author.
+
+  ------------------------------------------------------------------------------
+
+*/
+
+#if defined (VM_PDP11)
+#include "pdp11_defs.h"
+
+#elif defined (VM_PDP10)
+#include "pdp10_defs.h"
+
+#elif defined (VM_VAX)
+#include "vax_defs.h"
+
+#else
+#error The CH11 device only works with Unibus machines.
+#endif
+
+#include "sim_tmxr.h"
+
+/* CSR bits */
+#define TIE   0000001 /* Timer interrupt enable */
+#define LOOP  0000002 /* Loop back */
+#define SPY   0000004 /* Loop back */
+#define CRX   0000010 /* Clear receiver */
+#define RXIE  0000020 /* Receive interrupt enable */
+#define TXIE  0000040 /* Transmit interrupt enable */
+#define TXA   0000100 /* Transmit abort */
+#define TXD   0000200 /* Transmit done */
+#define CTX   0000400 /* Clear transmitter */
+#define LOST  0017000 /* Lost count */
+#define RESET 0020000 /* Reset */
+#define CRC   0040000 /* CRC error */
+#define RXD   0100000 /* Receive done */
+
+#define STATUS_BITS (TIE|LOOP|SPY|RXIE|TXIE|TXA|TXD|LOST|CRC|RXD)
+#define COMMAND_BITS (TIE|LOOP|SPY|RXIE|TXIE)
+
+BITFIELD ch_csr_bits[] = {
+  BIT(TIE),
+  BIT(LOOP),
+  BIT(SPY),
+  BIT(CRX),
+  BIT(RXIE),
+  BIT(TXIE),
+  BIT(TXA),
+  BIT(TXD),
+  BIT(CTX),
+  BITF(LOST,4),
+  BIT(RESET),
+  BIT(CRC),
+  BIT(RXD),
+  ENDBITS
+};
+
+#define CHUDP_HEADER 4
+#define IOLN_CH 020
+#define DBG_TRC  0x0001
+#define DBG_REG  0x0002
+#define DBG_PKT  0x0004
+#define DBG_DAT  0x0008
+#define DBG_INT  0x0010
+#define DBG_ERR  0x0020
+
+t_stat ch_svc(UNIT *);
+t_stat ch_reset (DEVICE *);
+t_stat ch_attach (UNIT *, CONST char *);
+t_stat ch_detach (UNIT *);
+t_stat ch_rd(int32 *, int32, int32);
+t_stat ch_wr(int32, int32, int32);
+t_stat ch_show_peer (FILE* st, UNIT* uptr, int32 val, CONST void* desc);
+t_stat ch_set_peer (UNIT* uptr, int32 val, CONST char* cptr, void* desc);
+t_stat ch_show_node (FILE* st, UNIT* uptr, int32 val, CONST void* desc);
+t_stat ch_set_node (UNIT* uptr, int32 val, CONST char* cptr, void* desc);
+t_stat ch_help (FILE *, DEVICE *, UNIT *, int32, const char *);
+t_stat ch_help_attach (FILE *, DEVICE *, UNIT *, int32, const char *);
+const char *ch_description (DEVICE *);
+
+static char peer[256];
+static int status;
+static int address = -1;
+static int rx_count;
+static int tx_count;
+static uint8 rx_buffer[512+100];
+static uint8 tx_buffer[512+100];
+
+TMLN ch_lines[1] = { {0} };
+TMXR ch_tmxr = { 1, NULL, 0, ch_lines};
+
+UNIT ch_unit[] = {
+  { UDATA (&ch_svc, UNIT_IDLE|UNIT_ATTABLE, 0) },
+};
+
+REG ch_reg[] = {
+  { GRDATADF(CSR,   status,     16, 16, 0, "Control and status", ch_csr_bits), REG_FIT },
+  { GRDATAD(RXCNT,  rx_count,   16, 16, 0, "Receive word count"), REG_FIT|REG_RO},
+  { GRDATAD(TXCNT,  tx_count,   16, 16, 0, "Transmit word count"), REG_FIT|REG_RO},
+  { BRDATAD(RXBUF,  rx_buffer,  16,  8, sizeof rx_buffer, "Receive packet buffer"), REG_FIT},
+  { BRDATAD(TXBUF,  tx_buffer,  16,  8, sizeof tx_buffer, "Transmit packet buffer"), REG_FIT},
+  { BRDATAD(PEER,   peer,       16,  8, sizeof peer, "Network peer"), REG_HRO},
+  { GRDATAD(NODE,   address,    16, 16, 0, "Node address"), REG_HRO},
+  { NULL }  };
+
+MTAB ch_mod[] = {
+  { MTAB_XTD|MTAB_VDV|MTAB_VALR, 010, "ADDRESS", "ADDRESS",
+    &set_addr, &show_addr, NULL, "Unibus address" },
+  { MTAB_XTD|MTAB_VDV|MTAB_VALR, 0, "VECTOR", "VECTOR",
+    &set_vec, &show_vec, NULL, "Interrupt vector" },
+  { MTAB_XTD|MTAB_VDV|MTAB_VALR, 0, "PEER", "PEER",
+    &ch_set_peer, &ch_show_peer, NULL, "Remote host name and port" },
+  { MTAB_XTD|MTAB_VDV|MTAB_VALR, 0, "NODE", "NODE",
+    &ch_set_node, &ch_show_node, NULL, "Chaosnet node address" },
+  { 0 },
+};
+
+DIB ch_dib = {
+  IOBA_AUTO, IOLN_CH, &ch_rd, &ch_wr,
+  1, IVCL (CH), VEC_AUTO
+};
+
+DEBTAB ch_debug[] = {
+    { "TRC",       DBG_TRC,   "Detailed trace" },
+    { "REG",       DBG_REG,   "Hardware registers" },
+    { "PKT",       DBG_PKT,   "Packets" },
+    { "DAT",       DBG_DAT,   "Packet data" },
+    { "INT",       DBG_INT,   "Interrupts" },
+    { "ERR",       DBG_ERR,   "Error conditions" },
+    { 0 }
+};
+
+DEVICE ch_dev = {
+    "CH", ch_unit, ch_reg, ch_mod,
+    1, 8, 16, 1, 8, 16,
+    NULL, NULL, &ch_reset,
+    NULL, &ch_attach, &ch_detach,
+    &ch_dib, DEV_DISABLE | DEV_DIS | DEV_UBUS | DEV_DEBUG,
+    0, ch_debug, NULL, NULL, &ch_help, &ch_help_attach, NULL,
+    &ch_description
+  };
+
+int ch_checksum (const uint8 *p, int length)
+{
+  int i, sum = 0;
+  for (i = 0; i < length; i += 2)
+    sum += (p[i] << 8) + p[i+1];
+  while (sum > 0xffff)
+    sum = (sum & 0xffff) + (sum >> 16);
+  return sum ^ 0xffff;
+}
+
+t_stat ch_rx_word (int32 *data)
+{
+  if (rx_count == 0) {
+    *data = 0;
+    sim_debug (DBG_ERR, &ch_dev, "Read empty buffer\n");
+  } else {
+    int i = 512-2*rx_count;
+    *data = (rx_buffer[i] << 8) + rx_buffer[i+1];
+    sim_debug (DBG_DAT, &ch_dev, "Read buffer word %d: %06o\n",
+               rx_count, *data);
+    rx_count--;
+  }
+  return SCPE_OK;
+}
+
+t_stat ch_tx_word (int data)
+{
+  if (tx_count < 126) {
+    int i = CHUDP_HEADER + 2*tx_count;
+    sim_debug (DBG_DAT, &ch_dev, "Write buffer word %d: %06o\n",
+               tx_count, data);
+    status &= ~TXD;
+    tx_buffer[i] = data >> 8;
+    tx_buffer[i+1] = data;
+    tx_count++;
+    return SCPE_OK;
+  } else {
+    sim_debug (DBG_ERR, &ch_dev, "Write buffer overflow\n");
+    return SCPE_INCOMP;
+  }
+}
+
+int ch_test_int (void)
+{
+  if ((status & (RXD|RXIE)) == (RXD|RXIE) ||
+      (status & (TXD|TXIE)) == (TXD|TXIE)) {
+    sim_debug (DBG_INT, &ch_dev, "%s %s Interrupt\n",
+               status & RXD ? "RX" : "",
+               status & TXD ? "TX" : "");
+    SET_INT(CH);
+    return 1;
+  } else {
+    CLR_INT(CH);
+    return 0;
+  }
+}
+
+t_stat ch_transmit ()
+{
+  size_t len;
+  t_stat r;
+
+  if (ch_tx_word (address) != SCPE_OK ||
+      ch_tx_word (ch_checksum (tx_buffer + CHUDP_HEADER, 2*tx_count)) != SCPE_OK)
+    return SCPE_INCOMP;
+
+  tmxr_poll_tx (&ch_tmxr);
+  len = CHUDP_HEADER + 2 * (size_t)tx_count;
+  r = tmxr_put_packet_ln (&ch_lines[0], (const uint8 *)&tx_buffer, len);
+  if (r == SCPE_OK) {
+    sim_debug (DBG_PKT, &ch_dev, "Sent UDP packet, %d bytes.\n", (int)len);
+    tmxr_poll_tx (&ch_tmxr);
+    status |= TXD;
+    ch_test_int ();
+  } else
+    sim_debug (DBG_ERR, &ch_dev, "Sending UDP failed: %d.\n", r);
+  return SCPE_OK;
+}
+
+void ch_validate (const uint8 *p, int count)
+{
+  int chksum;
+  int size;
+
+  sim_debug (DBG_TRC, &ch_dev, "Packet opcode: %02x\n", p[0]);
+  sim_debug (DBG_TRC, &ch_dev, "MBZ: %02x\n", p[1]);
+  sim_debug (DBG_TRC, &ch_dev, "Forwarding count: %02x\n", p[2] >> 4);
+  size = ((p[2] & 0xF) << 8) + p[3];
+  sim_debug (DBG_TRC, &ch_dev, "Packet size: %03x\n", size);
+  sim_debug (DBG_TRC, &ch_dev, "Destination address: %02x\n", (p[4] << 8) + p[5]);
+  sim_debug (DBG_TRC, &ch_dev, "Destination index: %02x\n", (p[6] << 8) + p[7]);
+  sim_debug (DBG_TRC, &ch_dev, "Source address: %02x\n", (p[8] << 8) + p[9]);
+  sim_debug (DBG_TRC, &ch_dev, "Source index: %02x\n", (p[10] << 8) + p[11]);
+  sim_debug (DBG_TRC, &ch_dev, "Packet number: %02x\n", (p[12] << 8) + p[13]);
+  sim_debug (DBG_TRC, &ch_dev, "Acknowledgement: %02x\n", (p[14] << 8) + p[15]);
+  
+  if (p[1] != 0)
+    sim_debug (DBG_ERR, &ch_dev, "Bad packet\n");
+
+  chksum = ch_checksum (p, count);
+  if (chksum != 0) {
+    sim_debug (DBG_ERR, &ch_dev, "Checksum error: %05o\n", chksum);
+    status |= CRC;
+  } else
+    sim_debug (DBG_TRC, &ch_dev, "Checksum: %05o\n", chksum);
+}
+
+void ch_receive (void)
+{
+  size_t count;
+  const uint8 *p;
+
+  tmxr_poll_rx (&ch_tmxr);
+  if (tmxr_get_packet_ln (&ch_lines[0], &p, &count) != SCPE_OK) {
+    sim_debug (DBG_ERR, &ch_dev, "TMXR error receiving packet\n");
+    return;
+  }
+  if (p == NULL)
+    return;
+
+  sim_debug (DBG_PKT, &ch_dev, "Received UDP packet, %d bytes\n", (int)count);
+  if ((status & RXD) == 0) {
+    count -= CHUDP_HEADER;
+    count = (count + 1) & 0776;
+    memcpy (rx_buffer + (512 - count), p + CHUDP_HEADER, count);
+    rx_count = count >> 1;
+    sim_debug (DBG_TRC, &ch_dev, "Rx count, %d\n", rx_count);
+    ch_validate (p + CHUDP_HEADER, count);
+    status |= RXD;
+    ch_lines[0].rcve = FALSE;
+    sim_debug (DBG_TRC, &ch_dev, "Rx off\n");
+    ch_test_int ();
+  } else {
+    sim_debug (DBG_ERR, &ch_dev, "Lost packet\n");
+    if ((status & LOST) < LOST)
+      status += 01000;
+  }
+}
+
+t_stat ch_rd (int32 *data, int32 PA, int32 access)
+{
+  int reg = (PA >> 1) & 07;
+
+  switch (reg) {
+  case 00: /* Status */
+    *data = status & STATUS_BITS;
+    sim_debug (DBG_REG, &ch_dev, "Read status: %06o\n", *data);
+    sim_debug_bits (DBG_TRC, &ch_dev, ch_csr_bits, *data, *data, TRUE);
+    break;
+  case 01: /* Address */
+    *data = address;
+    sim_debug (DBG_REG, &ch_dev, "Read address: %06o\n", *data);
+    break;
+  case 02: /* Read buffer */
+    return ch_rx_word (data);
+  case 03: /* Count */
+    *data = ((16 * rx_count) - 1) & 07777;
+    sim_debug (DBG_REG, &ch_dev, "Read bit count: %d\n", *data);
+    break;
+  case 05: /* Start */
+    sim_debug (DBG_REG, &ch_dev, "Start transmission\n");
+    *data = address;
+    return ch_transmit ();
+  default:
+    *data = 0;
+    break;
+  }
+
+  return SCPE_OK;
+}
+
+void ch_clear (void)
+{
+  status = 0;
+  rx_count = 0;
+  tx_count = 0;
+
+  tx_buffer[0] = 1; /* CHUDP header */
+  tx_buffer[1] = 1;
+  tx_buffer[2] = 0;
+  tx_buffer[3] = 0;
+
+  ch_test_int ();
+}
+
+void ch_command (int32 data)
+{
+  if (data & RESET) {
+    /* Do this first so other bits can do their things. */
+    sim_debug (DBG_REG, &ch_dev, "Reset\n");
+    ch_clear ();
+  }
+  if (data & CRX) {
+    sim_debug (DBG_REG, &ch_dev, "Clear RX\n");
+    rx_count = 0;
+    status &= ~(RXD|CRC|LOST);
+    ch_lines[0].rcve = TRUE;
+    sim_debug (DBG_TRC, &ch_dev, "Rx on\n");
+    sim_activate_abs (ch_unit, 100);   /* Force next packet read attempt */
+  }
+  if (data & CTX) {
+    sim_debug (DBG_REG, &ch_dev, "Clear TX\n");
+    tx_count = 0;
+    status |= TXD;
+    status &= ~TXA;
+  }
+  ch_test_int ();
+}
+
+t_stat ch_wr (int32 data, int32 PA, int32 access)
+{
+  int reg = (PA >> 1) & 07;
+
+  switch (reg) {
+  case 00: /* Command */
+    ch_command (data); /* Do this first in case of reset. */
+    if (data & TIE)
+      sim_debug (DBG_REG, &ch_dev, "Timer interrupt enable\n");
+    if (data & LOOP)
+      sim_debug (DBG_REG, &ch_dev, "Loopback\n");
+    if (data & SPY)
+      sim_debug (DBG_REG, &ch_dev, "Spy mode\n");
+    if (data & RXIE)
+      sim_debug (DBG_REG, &ch_dev, "RX interrupt enable\n");
+    if (data & TXIE)
+      sim_debug (DBG_REG, &ch_dev, "TX interrupt enable\n");
+    status = (status & ~COMMAND_BITS) | (data & COMMAND_BITS);
+    sim_debug_bits (DBG_TRC, &ch_dev, ch_csr_bits, status, status, TRUE);
+    ch_test_int ();
+    break;
+  case 01: /* Write */
+    return ch_tx_word (data);
+  }
+
+  return SCPE_OK;
+}
+
+t_stat ch_svc(UNIT *uptr)
+{
+  sim_clock_coschedule (uptr, 1000);
+  tmxr_poll_conn (&ch_tmxr);
+  if (ch_lines[0].conn)
+    ch_receive ();
+  return SCPE_OK;
+}
+
+t_stat ch_attach (UNIT *uptr, CONST char *cptr)
+{
+  char linkinfo[256];
+  t_stat r;
+
+  if (address == -1)
+    return sim_messagef (SCPE_2FARG, "Must set Chaosnet NODE address first \"SET CH NODE=val\"\n");
+  if (peer[0] == '\0')
+    return sim_messagef (SCPE_2FARG, "Must set Chaosnet PEER \"SET CH PEER=host:port\"\n");
+
+  sprintf (linkinfo, "Buffer=%d,Line=%d,UDP,%s,PACKET,Connect=%s",
+           (int)sizeof tx_buffer, 0, cptr, peer);
+  r = tmxr_attach (&ch_tmxr, uptr, linkinfo);
+  if (r != SCPE_OK) {
+    sim_debug (DBG_ERR, &ch_dev, "TMXR error opening master\n");
+    return sim_messagef (r, "Error Opening: %s\n", peer);
+  }
+
+  uptr->filename = (char *)realloc (uptr->filename, 1 + strlen (cptr));
+  strcpy (uptr->filename, cptr);
+  sim_clock_coschedule (uptr, 1000);
+  return SCPE_OK;
+}
+
+t_stat ch_detach (UNIT *uptr)
+{
+  sim_cancel (uptr);
+  tmxr_detach (&ch_tmxr, uptr);
+  return SCPE_OK;
+}
+
+t_stat ch_reset (DEVICE *dptr)
+{
+  ch_clear ();
+  return auto_config (dptr->name, (dptr->flags & DEV_DIS)? 0 : 1);  /* auto config */
+}
+
+t_stat ch_show_peer (FILE* st, UNIT* uptr, int32 val, CONST void* desc)
+{
+  fprintf (st, "peer=%s", peer);
+  return SCPE_OK;
+}
+
+t_stat ch_set_peer (UNIT* uptr, int32 val, CONST char* cptr, void* desc)
+{
+  char host[256], port[256];
+
+  if ((cptr == NULL) || (*cptr == 0))
+    return SCPE_ARG;
+  if (uptr->flags & UNIT_ATT)
+    return SCPE_ALATT;
+  if (sim_parse_addr (cptr, host, sizeof host, NULL, port, sizeof port, NULL, NULL))
+    return SCPE_ARG;
+  if (host[0] == '\0')
+    return SCPE_ARG;
+
+  strncpy (peer, cptr, sizeof peer);
+  return SCPE_OK;
+}
+
+t_stat ch_show_node (FILE* st, UNIT* uptr, int32 val, CONST void* desc)
+{
+  fprintf (st, "node=%o", address);
+  return SCPE_OK;
+}
+
+t_stat ch_set_node (UNIT* uptr, int32 val, CONST char* cptr, void* desc)
+{
+  t_stat r;
+  int x;
+
+  if ((cptr == NULL) || (*cptr == 0))
+    return SCPE_ARG;
+  if (uptr->flags & UNIT_ATT)
+    return SCPE_ALATT;
+
+  x = (int)get_uint (cptr, 8, 0177777, &r);
+  if (r != SCPE_OK)
+    return SCPE_ARG;
+
+  address = x;
+  return SCPE_OK;
+}
+
+const char *ch_description (DEVICE *dptr)
+{
+  return "CH11 Chaosnet interface";
+}
+
+t_stat ch_help (FILE *st, DEVICE *dptr, UNIT *uptr, int32 flag, const char *cptr)
+{
+  fprintf (st, "CH11 Chaosnet interface\n\n");
+  fprintf (st, "The CH11 is a Unibus device which can be used with PDP-11, VAX, and\n");
+  fprintf (st, "KS10.  It's a network interface for MIT's Chaosnet.  Options allow\n");
+  fprintf (st, "control of the node address and network peer.  The node address must\n");
+  fprintf (st, "be a 16-bit octal number.\n");
+  fprint_set_help (st, dptr);
+  fprintf (st, "\nConfigured options and controller state can be displayed with:\n");
+  fprint_show_help (st, dptr);
+  fprintf (st, "\nThe CH11 simulation will encapsulate Chaosnet packets in UDP or TCP.\n");
+  fprintf (st, "To access the network, the simulated Chaosnet interface must be attached\n");
+  fprintf (st, "to a network peer.\n\n");
+  ch_help_attach (st, dptr, uptr, flag, cptr);
+  fprintf (st, "Software that runs on SIMH that supports this device include:\n");
+  fprintf (st, " - ITS, the PDP-10 Incompatible Timesharing System\n");
+  fprintf (st, " - Berkeley Unix with MIT patches\n");
+  fprintf (st, " - MINITS, a PDP-11 Chaosnet router/terminal concentrator\n\n");
+  fprintf (st, "Outside SIMH, there's KLH10 and Lisp machine simulators.  Various\n");
+  fprintf (st, "encapsulating transport mechanisms exist: UDP, IP, Ethernet.\n\n");
+  fprintf (st, "Documentation:\n");
+  fprintf (st, "https://lm-3.github.io/amber.html#Hardware-Programming-Documentation\n\n");
+  return SCPE_OK;
+}
+
+t_stat ch_help_attach (FILE *st, DEVICE *dptr, UNIT *uptr, int32 flag, const char *cptr)
+{
+  fprintf (st, "To configure CH11, first set the local Chaosnet node address, and\n");
+  fprintf (st, "the peer:\n\n");
+  fprintf (st, "  sim> SET CH NODE=<octal address>\n");
+  fprintf (st, "  sim> SET CH PEER=<remote host>:<remote port>\n\n");
+  fprintf (st, "Then, attach a local port.  By default UDP is used:\n\n");
+  fprintf (st, "  sim> ATTACH CH <local port>\n\n");
+  fprintf (st, "If TCP is desired, add \"TCP\":\n\n");
+  fprintf (st, "  sim> ATTACH CH <local port>,TCP\n\n");
+  return SCPE_OK;
+}
diff --git a/PDP11/pdp11_defs.h b/PDP11/pdp11_defs.h
index 868d47ac..fb0a86f0 100644
--- a/PDP11/pdp11_defs.h
+++ b/PDP11/pdp11_defs.h
@@ -631,6 +631,7 @@ typedef struct pdp_dib DIB;
 #define INT_V_KMCA      23
 #define INT_V_KMCB      24
 #define INT_V_UCB       25
+#define INT_V_CH        26
 
 #define INT_V_PIR4      0                               /* BR4 */
 #define INT_V_TTI       1
@@ -716,6 +717,7 @@ typedef struct pdp_dib DIB;
 #define INT_PIR1        (1u << INT_V_PIR1)
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define INT_INTERNAL7   (INT_PIR7)
 #define INT_INTERNAL6   (INT_PIR6 | INT_CLK)
@@ -745,6 +747,7 @@ typedef struct pdp_dib DIB;
 #define IPL_RY          5
 #define IPL_XQ          5
 #define IPL_XU          5
+#define IPL_CH          5
 #define IPL_TU          5
 #define IPL_RF          5
 #define IPL_RC          5
diff --git a/PDP11/pdp11_io_lib.c b/PDP11/pdp11_io_lib.c
index 42b51635..8ca3b9c7 100644
--- a/PDP11/pdp11_io_lib.c
+++ b/PDP11/pdp11_io_lib.c
@@ -777,6 +777,8 @@ AUTO_CON auto_tab[] = {/*c  #v  am vm  fxa   fxv */
     { { NULL },          1,  2,  4, 8 },                /* DTC05, DECvoice */
     { { NULL },          1,  2,  8, 8 },                /* KWV32 (DSV11) */
     { { NULL },          1,  1, 64, 4 },                /* QZA */
+    { { "CH" },          1,  1,  0, 0, 
+        {04140}, {0270} },                              /* CH11 - CHAOS Net - fx CSR, fx VEC */
     { { NULL },         -1 }                            /* end table */
 };
 
diff --git a/PDP11/pdp11_sys.c b/PDP11/pdp11_sys.c
index 5bb036a9..8d791ba9 100644
--- a/PDP11/pdp11_sys.c
+++ b/PDP11/pdp11_sys.c
@@ -117,6 +117,7 @@ extern DEVICE dpv_dev;
 extern DEVICE kmc_dev;
 extern DEVICE uca_dev, ucb_dev;
 extern DEVICE rom_dev;
+extern DEVICE ch_dev;
 extern REG cpu_reg[];
 extern int32 saved_PC;
 
@@ -195,6 +196,7 @@ DEVICE *sim_devices[] = {
     &kmc_dev,
     &ke_dev,
     &rom_dev,
+    &ch_dev,
 #else
     &clk_dev,
     &tti_dev,
diff --git a/VAX/vax730_defs.h b/VAX/vax730_defs.h
index 19bb1731..8e9fd8db 100644
--- a/VAX/vax730_defs.h
+++ b/VAX/vax730_defs.h
@@ -277,6 +277,7 @@ typedef struct {
 #define INT_V_DUPRX     12
 #define INT_V_DUPTX     13
 #define INT_V_RK        14
+#define INT_V_CH        15
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -311,6 +312,7 @@ typedef struct {
 #define INT_RK          (1u << INT_V_RK)
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -323,6 +325,7 @@ typedef struct {
 #define IPL_TS          (0x15 - IPL_HMIN)
 #define IPL_RY          (0x15 - IPL_HMIN)
 #define IPL_XU          (0x15 - IPL_HMIN)
+#define IPL_CH          (0x15 - IPL_HMIN)
 #define IPL_RB          (0x15 - IPL_HMIN)
 #define IPL_LPT         (0x14 - IPL_HMIN)
 #define IPL_PTR         (0x14 - IPL_HMIN)
diff --git a/VAX/vax730_syslist.c b/VAX/vax730_syslist.c
index f1d779e3..99c4a066 100644
--- a/VAX/vax730_syslist.c
+++ b/VAX/vax730_syslist.c
@@ -56,6 +56,7 @@ extern DEVICE dz_dev;
 extern DEVICE vh_dev;
 extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
+extern DEVICE ch_dev;
 
 DEVICE *sim_devices[] = { 
     &cpu_dev,
@@ -88,6 +89,7 @@ DEVICE *sim_devices[] = {
     &xu_dev,
     &xub_dev,
     &dmc_dev,
+    &ch_dev,
     NULL
     };
 
diff --git a/VAX/vax750_defs.h b/VAX/vax750_defs.h
index d34c1ae1..23609675 100644
--- a/VAX/vax750_defs.h
+++ b/VAX/vax750_defs.h
@@ -318,6 +318,7 @@ typedef struct {
 #define INT_V_DUPRX     11
 #define INT_V_DUPTX     12
 #define INT_V_RK        13
+#define INT_V_CH        14
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -351,6 +352,7 @@ typedef struct {
 #define INT_RK          (1u << INT_V_RK)
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -363,6 +365,7 @@ typedef struct {
 #define IPL_TS          (0x15 - IPL_HMIN)
 #define IPL_RY          (0x15 - IPL_HMIN)
 #define IPL_XU          (0x15 - IPL_HMIN)
+#define IPL_CH          (0x15 - IPL_HMIN)
 #define IPL_LPT         (0x14 - IPL_HMIN)
 #define IPL_PTR         (0x14 - IPL_HMIN)
 #define IPL_PTP         (0x14 - IPL_HMIN)
diff --git a/VAX/vax750_syslist.c b/VAX/vax750_syslist.c
index 9c409a31..e2ac0c7b 100644
--- a/VAX/vax750_syslist.c
+++ b/VAX/vax750_syslist.c
@@ -58,6 +58,7 @@ extern DEVICE dz_dev;
 extern DEVICE vh_dev;
 extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
+extern DEVICE ch_dev;
 
 DEVICE *sim_devices[] = { 
     &cpu_dev,
@@ -93,6 +94,7 @@ DEVICE *sim_devices[] = {
     &xu_dev,
     &xub_dev,
     &dmc_dev,
+    &ch_dev,
     NULL
     };
 
diff --git a/VAX/vax780_defs.h b/VAX/vax780_defs.h
index 77b91597..4ddf47a1 100644
--- a/VAX/vax780_defs.h
+++ b/VAX/vax780_defs.h
@@ -335,6 +335,7 @@ typedef struct {
 #define INT_V_DUPRX     11
 #define INT_V_DUPTX     12
 #define INT_V_RK        13
+#define INT_V_CH        14
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -368,6 +369,7 @@ typedef struct {
 #define INT_RK          (1u << INT_V_RK)
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -380,6 +382,7 @@ typedef struct {
 #define IPL_TS          (0x15 - IPL_HMIN)
 #define IPL_RY          (0x15 - IPL_HMIN)
 #define IPL_XU          (0x15 - IPL_HMIN)
+#define IPL_CH          (0x15 - IPL_HMIN)
 #define IPL_LPT         (0x14 - IPL_HMIN)
 #define IPL_PTR         (0x14 - IPL_HMIN)
 #define IPL_PTP         (0x14 - IPL_HMIN)
diff --git a/VAX/vax780_syslist.c b/VAX/vax780_syslist.c
index 81dbdbae..2b87a97b 100644
--- a/VAX/vax780_syslist.c
+++ b/VAX/vax780_syslist.c
@@ -65,6 +65,7 @@ extern DEVICE dz_dev;
 extern DEVICE vh_dev;
 extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
+extern DEVICE ch_dev;
 
 DEVICE *sim_devices[] = { 
     &cpu_dev,
@@ -101,6 +102,7 @@ DEVICE *sim_devices[] = {
     &xu_dev,
     &xub_dev,
     &dmc_dev,
+    &ch_dev,
     NULL
     };
 
diff --git a/VAX/vax860_defs.h b/VAX/vax860_defs.h
index 76ec956d..758e2b08 100644
--- a/VAX/vax860_defs.h
+++ b/VAX/vax860_defs.h
@@ -362,6 +362,7 @@ typedef struct {
 #define INT_V_DUPRX     11
 #define INT_V_DUPTX     12
 #define INT_V_RK        13
+#define INT_V_CH        14
 
 #define INT_V_LPT       0                               /* BR4 */
 #define INT_V_PTR       1
@@ -395,6 +396,7 @@ typedef struct {
 #define INT_RK          (1u << INT_V_RK)
 #define INT_TDRX        (1u << INT_V_TDRX)
 #define INT_TDTX        (1u << INT_V_TDTX)
+#define INT_CH          (1u << INT_V_CH)
 
 #define IPL_DTA         (0x16 - IPL_HMIN)
 #define IPL_CR          (0x16 - IPL_HMIN)
@@ -407,6 +409,7 @@ typedef struct {
 #define IPL_TS          (0x15 - IPL_HMIN)
 #define IPL_RY          (0x15 - IPL_HMIN)
 #define IPL_XU          (0x15 - IPL_HMIN)
+#define IPL_CH          (0x15 - IPL_HMIN)
 #define IPL_LPT         (0x14 - IPL_HMIN)
 #define IPL_PTR         (0x14 - IPL_HMIN)
 #define IPL_PTP         (0x14 - IPL_HMIN)
diff --git a/VAX/vax860_syslist.c b/VAX/vax860_syslist.c
index a0c6f3db..7dcb8709 100644
--- a/VAX/vax860_syslist.c
+++ b/VAX/vax860_syslist.c
@@ -65,6 +65,7 @@ extern DEVICE dz_dev;
 extern DEVICE vh_dev;
 extern DEVICE xu_dev, xub_dev;
 extern DEVICE dmc_dev;
+extern DEVICE ch_dev;
 
 DEVICE *sim_devices[] = { 
     &cpu_dev,
@@ -100,6 +101,7 @@ DEVICE *sim_devices[] = {
     &xu_dev,
     &xub_dev,
     &dmc_dev,
+    &ch_dev,
     NULL
     };
 
diff --git a/makefile b/makefile
index b1bd05ed..8d160a07 100644
--- a/makefile
+++ b/makefile
@@ -1222,7 +1222,7 @@ PDP11 = ${PDP11D}/pdp11_fp.c ${PDP11D}/pdp11_cpu.c ${PDP11D}/pdp11_dz.c \
 	${PDP11D}/pdp11_ke.c ${PDP11D}/pdp11_dc.c ${PDP11D}/pdp11_dmc.c \
 	${PDP11D}/pdp11_kmc.c ${PDP11D}/pdp11_dup.c ${PDP11D}/pdp11_rs.c \
 	${PDP11D}/pdp11_vt.c ${PDP11D}/pdp11_td.c ${PDP11D}/pdp11_io_lib.c \
-	${PDP11D}/pdp11_rom.c $(DISPLAYL) $(DISPLAYVT)
+	${PDP11D}/pdp11_rom.c ${PDP11D}/pdp11_ch.c $(DISPLAYL) $(DISPLAYVT)
 PDP11_OPT = -DVM_PDP11 -I ${PDP11D} ${NETWORK_OPT} $(DISPLAY_OPT)
 
 
@@ -1287,7 +1287,7 @@ VAX730 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${PDP11D}/pdp11_xu.c ${PDP11D}/pdp11_ry.c ${PDP11D}/pdp11_cr.c \
 	${PDP11D}/pdp11_hk.c ${PDP11D}/pdp11_vh.c ${PDP11D}/pdp11_dmc.c \
 	${PDP11D}/pdp11_td.c ${PDP11D}/pdp11_tc.c ${PDP11D}/pdp11_rk.c \
-	${PDP11D}/pdp11_io_lib.c
+	${PDP11D}/pdp11_io_lib.c ${PDP11D}/pdp11_ch.c
 VAX730_OPT = -DVM_VAX -DVAX_730 -DUSE_INT64 -DUSE_ADDR64 -I VAX -I ${PDP11D} ${NETWORK_OPT}
 
 
@@ -1303,7 +1303,7 @@ VAX750 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${PDP11D}/pdp11_hk.c ${PDP11D}/pdp11_rp.c ${PDP11D}/pdp11_tu.c \
 	${PDP11D}/pdp11_vh.c ${PDP11D}/pdp11_dmc.c ${PDP11D}/pdp11_dup.c \
 	${PDP11D}/pdp11_td.c ${PDP11D}/pdp11_tc.c ${PDP11D}/pdp11_rk.c \
-	${PDP11D}/pdp11_io_lib.c
+	${PDP11D}/pdp11_io_lib.c ${PDP11D}/pdp11_ch.c
 VAX750_OPT = -DVM_VAX -DVAX_750 -DUSE_INT64 -DUSE_ADDR64 -I VAX -I ${PDP11D} ${NETWORK_OPT}
 
 
@@ -1319,7 +1319,7 @@ VAX780 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${PDP11D}/pdp11_rp.c ${PDP11D}/pdp11_tu.c ${PDP11D}/pdp11_hk.c \
 	${PDP11D}/pdp11_vh.c ${PDP11D}/pdp11_dmc.c ${PDP11D}/pdp11_dup.c \
 	${PDP11D}/pdp11_td.c ${PDP11D}/pdp11_tc.c ${PDP11D}/pdp11_rk.c \
-	${PDP11D}/pdp11_io_lib.c
+	${PDP11D}/pdp11_io_lib.c ${PDP11D}/pdp11_ch.c
 VAX780_OPT = -DVM_VAX -DVAX_780 -DUSE_INT64 -DUSE_ADDR64 -I VAX -I ${PDP11D} ${NETWORK_OPT}
 
 
@@ -1335,7 +1335,7 @@ VAX8600 = ${VAXD}/vax_cpu.c ${VAXD}/vax_cpu1.c ${VAXD}/vax_fpa.c \
 	${PDP11D}/pdp11_rp.c ${PDP11D}/pdp11_tu.c ${PDP11D}/pdp11_hk.c \
 	${PDP11D}/pdp11_vh.c ${PDP11D}/pdp11_dmc.c ${PDP11D}/pdp11_dup.c \
 	${PDP11D}/pdp11_td.c ${PDP11D}/pdp11_tc.c ${PDP11D}/pdp11_rk.c \
-	${PDP11D}/pdp11_io_lib.c
+	${PDP11D}/pdp11_io_lib.c ${PDP11D}/pdp11_ch.c
 VAX8600_OPT = -DVM_VAX -DVAX_860 -DUSE_INT64 -DUSE_ADDR64 -I VAX -I ${PDP11D} ${NETWORK_OPT}
 
 
@@ -1346,7 +1346,7 @@ PDP10 = ${PDP10D}/pdp10_fe.c ${PDP11D}/pdp11_dz.c ${PDP10D}/pdp10_cpu.c \
 	${PDP10D}/pdp10_tim.c ${PDP10D}/pdp10_tu.c ${PDP10D}/pdp10_xtnd.c \
 	${PDP11D}/pdp11_pt.c ${PDP11D}/pdp11_ry.c ${PDP11D}/pdp11_cr.c \
 	${PDP11D}/pdp11_dup.c ${PDP11D}/pdp11_dmc.c ${PDP11D}/pdp11_kmc.c \
-	${PDP11D}/pdp11_xu.c
+	${PDP11D}/pdp11_xu.c ${PDP11D}/pdp11_ch.c
 PDP10_OPT = -DVM_PDP10 -DUSE_INT64 -I ${PDP10D} -I ${PDP11D} ${NETWORK_OPT}