diff --git a/tools/a7out b/tools/a7out
index 616711b..ee77652 100755
--- a/tools/a7out
+++ b/tools/a7out
@@ -86,9 +86,9 @@ sub simulate {
         my $opcode      = ( $instruction >> 12 ) & 074;
         my $indirect    = ( $instruction >> 13 ) & 1;
         my $addr        = $instruction & 017777;
-        printf( "PC %06o: instruction %08o, op %03o, ind %o, addr %06o\n",
-            $PC, $instruction, $opcode, $indirect, $addr )
-          if ($debug);
+        #printf( "PC %06o: instruction %08o, op %03o, ind %o, addr %06o\n",
+        #    $PC, $instruction, $opcode, $indirect, $addr )
+        #  if ($debug);
 
         # Simulate the instruction. Each subroutine updates the $PC
         if ( defined( $Oplist{$opcode} ) ) {
@@ -163,14 +163,14 @@ sub iot {
     if ( defined( $Syscallist{$addr} ) ) {
         $Syscallist{$addr}->();
     } else {
-        printf( "Unknown syscall %d at location 0%o\n", $addr, $PC );
+        printf( "PC %06o: Unknown syscall %d\n", $PC, $addr );
         die("\n");
     }
 }
 
 # Exit system call
 sub sys_exit {
-  print("exit system call\n") if ($debug);
+  printf("PC %06o: exit system call\n", $PC) if ($debug);
   exit(0);
 }
 
@@ -178,7 +178,7 @@ sub sys_exit {
 sub sys_close {
   # AC is the file descriptor
   my $fd= $AC;
-  print("close: closing fd $fd\n") if ($debug);
+  printf("PC %06o: close: closing fd %d\n", $PC, $fd) if ($debug);
 
   # Bump up the PC
   $PC += 1;
@@ -207,24 +207,23 @@ sub sys_open {
 
   # Convert this to a sensible ASCII filename
   my $filename= mem2string($start);
-  printf("open: file %s\n", $filename) if ($debug);
+  printf("PC %06o: open: file %s\n", $PC, $filename) if ($debug);
 
-  open(my $FH, "<", $filename);
-
-  # No filehandle, so it's an error
-  if (!defined($FH)) {
+  # Open the file
+  if (open(my $FH, "<", $filename)) {
+    # Find a place in the @FD array to store this filehandle. 99 is arbitrary
+    my $fd;
+    foreach $fd (0 .. 99) {
+      if (!defined($FD[$fd])) {
+        $FD[$fd]= $FH; last;
+      }
+    }
+    $AC=$fd; return;
+  } else {
+    # No filehandle, so it's an error
     print("open failed: $!\n") if ($debug);
     $AC= 0777777; return;
   }
-
-  # Find a place in the @FD array to store this filehandle. 99 is arbitrary
-  my $fd;
-  foreach $fd (0 .. 99) {
-    if (!defined($FD[$fd])) {
-      $FD[$fd]= $FH; last;
-    }
-  }
-  $AC=$fd; return;
 }
 
 # Read system call
@@ -238,7 +237,7 @@ sub sys_read {
   my $start= $Mem[$PC+1];
   my $count= $Mem[$PC+2];
   my $end= $start + $count -1;
-  printf("read: %d words from %o from fd %d\n", $count, $start, $fd) if ($debug);
+  printf("PC %06o: read: %d words from %o from fd %d\n", $PC, $count, $start, $fd) if ($debug);
 
   # Bump up the PC
   $PC += 3;
@@ -284,7 +283,7 @@ sub sys_write {
   my $start= $Mem[$PC+1];
   my $count= $Mem[$PC+2];
   my $end= $start + $count -1;
-  printf("write: %d words from %o to fd %d\n", $count, $start, $fd) if ($debug);
+  printf("PC %06o: write: %d words from %o to fd %d\n", $PC, $count, $start, $fd) if ($debug);
 
   # Bump up the PC
   $PC += 3;
diff --git a/tools/as7 b/tools/as7
index 0e047fa..94ad9f4 100755
--- a/tools/as7
+++ b/tools/as7
@@ -26,8 +26,39 @@ my $stage = 1; # Pass one or pass two
 # Check the arguments
 die("Usage: $0 file1.s [file2.s ...]\n") if ( @ARGV < 1 );
 
-# Start with the location counter at zero
-$Var{'.'} = 0;
+# Define the syscalls as variables so that
+# I don't have to hand-code the logic below.
+# Also, start with the location counter at zero
+%Var= (
+  '.' => 0,
+  save => 1,
+  getuid => 2,
+  open => 3,
+  read => 4,
+  write => 5,
+  creat => 6,
+  seek => 7,
+  tell => 8,
+  close => 9,
+  link => 10,
+  unlink => 11,
+  setuid => 12,
+  rename => 13,
+  exit => 14,
+  time => 15,
+  intrp => 16,
+  chdir => 17,
+  chmod => 18,
+  chown => 19,
+  badcal => 20,
+  syslog => 21,
+  capt => 23,
+  rele => 24,
+  status => 25,
+  smes => 27,
+  rmes => 28,
+  fork => 29
+);
 
 # Parse all the files
 foreach my $file (@ARGV) {
@@ -189,6 +220,7 @@ sub parse_expression {
         'i'      => 0020000,
         'eae'    => 0640000,
         'iot'    => 0700000,
+        'sys'    => 0700000,
         'opr'    => 0740000,
         'law'    => 0760000,
         'lam'    => 0777777,
diff --git a/tools/write_test.s b/tools/write_test.s
index dd266e8..40706b1 100644
--- a/tools/write_test.s
+++ b/tools/write_test.s
@@ -7,16 +7,16 @@ main:
    lac in
    dac out
 
-   " The assembler doesn't know sys write, so iot 5 for now
+   " Write hello to fd1 i.e stdout
    lac d1
-   iot 5; hello; 7
+   sys write; hello; 7
 
    " open file fred
-   iot 3; fred; 0; 0
+   sys open; fred; 0; 0
 
    " read 5 words into the buffer from stdin: type in 10 or more characters!
    lac d0
-   iot 4; buf; 5
+   sys read; buf; 5
 
    " Stop and dump memory, so you can see five words at location 0400
    " Comment out the hlt instruction to test close and exit
@@ -24,10 +24,10 @@ main:
 
    " close stdin
    lac d0
-   iot 9
+   sys close
 
    " exit
-   iot 14
+   sys exit
 
    " We should not get to the halt instruction
    hlt
@@ -41,8 +41,6 @@ in: 023
 out: 0
 
 " Hello, world\n, two ASCII chars per word
-d0: 0
-d1: 1
 hello: 0110145; 0154154; 0157054; 040; 0167157; 0162154; 0144012
 
 " fred as a string, NUL terminated
@@ -51,3 +49,6 @@ fred: 0146162; 0145144; 0
 " Input buffer for read
 . = 0400
 buf: 0
+
+d0: 0
+d1: 1