diff --git a/H316/h316_hi.c b/H316/h316_hi.c
index 4b7874ec..a80a5912 100644
--- a/H316/h316_hi.c
+++ b/H316/h316_hi.c
@@ -268,7 +268,7 @@ void hi_link_error (uint16 line)
   //   Any physical I/O error, either for the UDP link or a COM port, prints a
   // message and detaches the modem.  It's up to the user to decide what to do
   // after that...
-  fprintf(stderr,"HI%d - UNRECOVERABLE I/O ERROR!\n", line);
+  sim_printf("HI%d - UNRECOVERABLE I/O ERROR!\n", line);
   hi_reset_rx(line);  hi_reset_tx(line);
   sim_cancel(PUNIT(line));  hi_detach(PUNIT(line));
   PHIDB(line)->link = NOLINK;
@@ -344,7 +344,6 @@ void hi_start_tx (uint16 line, uint16 flags)
     tmp [0] = flags;
     for (i = 0; i < count; i ++)
       tmp [i + 1] = M [next+i];
-    //ret = udp_send(PDEVICE(line), PHIDB(line)->link, &M[next], count);
     ret = udp_send(PDEVICE(line), PHIDB(line)->link, tmp, count);
     free (tmp);
     if (ret != SCPE_OK && ret != 66) hi_link_error(line);
@@ -359,8 +358,7 @@ void hi_start_tx (uint16 line, uint16 flags)
   // DLE, STX, ETX and checksum bytes, that would be added to the packet.
   nbits = (((uint32) count)*2UL + 12UL) * 8UL;
   PHIDB(line)->txdelay = (nbits * 1000000UL) / (PHIDB(line)->bps * rtc_interval);
-  //fprintf(stderr,"HI%d - transmit packet, length=%d, bits=%ld, interval=%ld, delay=%ld\n", line, count, nbits, rtc_interval, PHIDB(line)->txdelay);
-
+  sim_debug(IMP_DBG_IOT, PDEVICE(line), "HI%d - transmit packet, length=%d, bits=%ld, interval=%ld, delay=%ld\n", line, count, nbits, rtc_interval, PHIDB(line)->txdelay);
   // That's it - we're done until it's time for the TX done interrupt ...
   CLR_TX_IRQ(line);
 }
@@ -425,7 +423,6 @@ void hi_poll_rx (uint16 line)
   // Read the packet into a temp buffer for disassembly.
   tmp = (uint16 *)malloc (MAXDATA * sizeof (*tmp));
 
-  //count = udp_receive(PDEVICE(line), PHIDB(line)->link, pdata, maxbuf);
   count = udp_receive(PDEVICE(line), PHIDB(line)->link, tmp, maxbuf+1);
   if (count == 0) {free (tmp); return; }
   if (count < 0) {free (tmp); hi_link_error(line); return; }
@@ -533,7 +530,7 @@ int32 hi_io (uint16 host, int32 inst, int32 fnc, int32 dat, int32 dev)
         udp_set_link_loopback (PDEVICE(host), PHIDB(host)->link, FALSE);
         return dat;
       case 005:
-//fprintf (stderr, "HnENAB unimp.\r\n");
+        sim_printf("HnENAB unimp.\n");
         // HnENAB - enable ...
         sim_debug(IMP_DBG_IOT, PDEVICE(host), "enable host (PC=%06o)\n", PC-1);
         return dat;
@@ -550,7 +547,7 @@ int32 hi_io (uint16 host, int32 inst, int32 fnc, int32 dat, int32 dev)
       case 001:
         // HnRDY - skip on host ready ...
         //sim_debug(IMP_DBG_IOT, PDEVICE(host), "skip on ready (PC=%06o %s)\n", PC-1, PHIDB(host)->ready ? "SKIP" : "NOSKIP");
-//fprintf (stderr, "HnRDY unimpl.; always ready\r\n");
+        sim_printf("HnRDY unimpl.; always ready\n");
         return  PHIDB(host)->ready ? IOSKIP(dat) : dat;
       case 002:
         // HnEOM - skip on end of message ...
@@ -559,7 +556,7 @@ int32 hi_io (uint16 host, int32 inst, int32 fnc, int32 dat, int32 dev)
         return dat;
       case 005:
         // HnFULL - skip on host buffer full ...
-fprintf (stderr, "HnFULL unimp.\r\n");
+        sim_printf("HnFULL unimp.\n");
         sim_debug(IMP_DBG_IOT, PDEVICE(host), "skip on buffer full (PC=%06o %s)\n", PC-1, "NOSKIP");
         return dat;
     }
@@ -635,10 +632,8 @@ t_stat hi_attach (UNIT *uptr, CONST char *cptr)
   if ((uptr->flags & UNIT_ATT) != 0) detach_unit(uptr);
 
   // The physical (COM port) attach isn't implemented yet ...
-  if (fport) {
-    fprintf(stderr,"HI%d - physical COM support is not yet implemented\n", host);
-    return SCPE_ARG;
-  }
+  if (fport)
+    return sim_messagef(SCPE_ARG,"HI%d - physical COM support is not yet implemented\n", host);
 
   //   Make a copy of the "file name" argument.  udp_create() actually modifies
   // the string buffer we give it, so we make a copy now so we'll have something
diff --git a/H316/h316_mi.c b/H316/h316_mi.c
index 414ebde1..e9d79e73 100644
--- a/H316/h316_mi.c
+++ b/H316/h316_mi.c
@@ -367,7 +367,7 @@ void mi_link_error (uint16 line)
   //   Any physical I/O error, either for the UDP link or a COM port, prints a
   // message and detaches the modem.  It's up to the user to decide what to do
   // after that...
-  fprintf(stderr,"MI%d - UNRECOVERABLE I/O ERROR!\n", line);
+  sim_printf("MI%d - UNRECOVERABLE I/O ERROR!\n", line);
   mi_reset_rx(line);  mi_reset_tx(line);
   sim_cancel(PUNIT(line));  mi_detach(PUNIT(line));
   PMIDB(line)->link = NOLINK;
@@ -700,10 +700,8 @@ t_stat mi_attach (UNIT *uptr, CONST char *cptr)
   if ((uptr->flags & UNIT_ATT) != 0) detach_unit(uptr);
 
   // The physical (COM port) attach isn't implemented yet ...
-  if (fport) {
-    fprintf(stderr,"MI%d - physical COM support is not yet implemented\n", line);
-    return SCPE_ARG;
-  }
+  if (fport)
+    return sim_messagef(SCPE_ARG,"MI%d - physical COM support is not yet implemented\n", line);
 
   //   Make a copy of the "file name" argument.  udp_create() actually modifies
   // the string buffer we give it, so we make a copy now so we'll have something
diff --git a/H316/h316_rtc.c b/H316/h316_rtc.c
index e9a26934..1e267589 100644
--- a/H316/h316_rtc.c
+++ b/H316/h316_rtc.c
@@ -365,10 +365,8 @@ t_stat wdt_set_delay (UNIT *uptr, int32 val, CONST char *cptr, void *desc)
   if (cptr == NULL) return SCPE_ARG;
   newint = get_uint (cptr, 10, 65535, &ret);
   if (ret != SCPE_OK) return ret;
-  if (newint != 0) {
-    fprintf(stderr,"WDT - timeout not yet implemented\n");
-    return SCPE_IERR;
-  }
+  if (newint != 0)
+    return sim_messagef(SCPE_IERR, "WDT - timeout not yet implemented\n");
   wdt_delay = newint;
 // TBA add calculations here???
   return SCPE_OK;
diff --git a/H316/h316_udp.c b/H316/h316_udp.c
index 4d215555..a7f3c6ba 100644
--- a/H316/h316_udp.c
+++ b/H316/h316_udp.c
@@ -136,7 +136,6 @@
 
 // Local constants ...
 #define MAXLINKS        10      // maximum number of simultaneous connections
-
 // UDP connection data structure ...
 //   One of these blocks is allocated for every simulated modem link. 
 struct _UDP_LINK {
@@ -235,18 +234,11 @@ t_stat udp_parse_remote (int32 link, const char *premote)
 
   if ((strcmp (udp_links[link].lport, port) == 0) && 
       (strcmp ("localhost", host) == 0))
-    fprintf(stderr,"WARNING - use different transmit and receive ports!\n");
+    return sim_messagef (SCPE_ARG, "WARNING - use different transmit and receive ports!\n");
 
   return SCPE_OK;
 }
 
-t_stat udp_error (int32 link, const char *msg)
-{
-  // This routine is called whenever a SOCKET_ERROR is returned for any I/O.
-  fprintf(stderr,"UDP%d - %s failed with error %d\n", link, msg, WSAGetLastError());
-  return SCPE_IOERR;
-}
-
 t_stat udp_create (DEVICE *dptr, const char *premote, int32 *pln)
 {
   //   Create a logical UDP link to the specified remote system.  The "remote"
@@ -327,12 +319,7 @@ t_stat udp_send (DEVICE *dptr, int32 link, uint16 *pdata, uint16 count)
 
   // Send it and we're outta here ...
   iret = tmxr_put_packet_ln (&udp_lines[link], (const uint8 *)&pkt, (size_t)pktlen);
-  if (iret == 111)
-    {
-      fprintf (stderr, "link %d got connection refused\n", link);
-      return SCPE_OK;
-    }
-  if (iret != SCPE_OK) return udp_error(link, "tmxr_put_packet_ln()");
+  if (iret != SCPE_OK) return sim_messagef(iret, "UDP%d - tmxr_put_packet_ln() failed with error %s\n", link, sim_error_text(iret));
   sim_debug(IMP_DBG_UDP, dptr, "link %d - packet sent (sequence=%d, length=%d)\n", link, ntohl(pkt.sequence), ntohs(pkt.count));
   return SCPE_OK;
 }
@@ -366,7 +353,7 @@ int32 udp_receive_packet (int32 link, UDP_PACKET *ppkt)
   ret = tmxr_get_packet_ln (&udp_lines[link], &pbuf, &pktsiz);
   udp_lines[link].rcve = FALSE;          // Disable receiver
   if (ret != SCPE_OK) {
-    udp_error(link, "tmxr_get_packet_ln()");
+    sim_messagef (ret, "UDP%d - tmxr_get_packet_ln() failed with error %s\n", link, sim_error_text(ret));
     return NOLINK;
   }
   if (pbuf == NULL) return 0;