--- vt102/vt102	2014/12/01 18:31:02	1.4
+++ vt102/vt102	2014/12/01 18:41:36	1.5
@@ -34,8 +34,7 @@
 my $KBD   = 1;
 
 #############################################################################
-
-my $PTY; # the pty we allocated, if any
+# rom initialising
 
 my $ROM = do {
    binmode DATA;
@@ -58,7 +57,9 @@
 }
 
 #############################################################################
+# cpu registers and I/O support
 
+my $PTY; # the pty we allocated, if any
 my $PRSTATUS = 0;
 
 # 8080/8085 registers
@@ -75,6 +76,7 @@
 my $CLK; # rather inexact clock
 
 #############################################################################
+# the dreaded nvr1400 chip. not needed to get it going, but provided for reference
 
 # nvram
 my @NVR = (0x3fff) x 100; # vt102: 214e accum, 214f only lower 8 bit used, first 44 bytes
@@ -82,35 +84,15 @@
 my $NVRDATA;
 my $NVRLATCH;
 
-#$NVR[$_] = $_ for 0..99;#d#
-
 my @NVRCMD = (
-   sub { # accept data
-      $NVRDATA = ($NVRDATA << 1) + $_[1];
-   },
-   sub { # accept addr
-      $NVRADDR = ($NVRADDR << 1)+ $_[1];
-   },
-   sub { # shift out
-      my $bit = $NVRDATA & 0x02000;
-      $NVRDATA *= 2;
-      $bit
-   },
-   undef,
-   sub { # write
-      print "NVR WRITE $_[0]\n";#d#
-      $NVR[$_[0]] = $NVRDATA & 0x3fff;
-   },
-   sub { # erase
-      print "NVR ERASE $_[0]\n";#d#
-      $NVR[$_[0]] = 0x3fff;
-   },
-   sub { # read
-#      print "NVR READ $_[0] = $NVR[$_[0]]\n";#d#
-      $NVRDATA = $NVR[$_[0]];
-   },
-   sub { # standby
-   },
+   sub { $NVRDATA = ($NVRDATA << 1) + $_[1]; }, # 0 accept data
+   sub { $NVRADDR = ($NVRADDR << 1) + $_[1]; }, # 1 accept addr
+   sub { ($NVRDATA <<= 1) & 0x4000 },           # 2 shift out
+   undef,                                       # 3 not used, will barf
+   sub { $NVR[$_[0]] = $NVRDATA & 0x3fff; },    # 4 write
+   sub { $NVR[$_[0]] = 0x3fff;            },    # 5 erase
+   sub { $NVRDATA = $NVR[$_[0]];          },    # 6 read
+   sub { },                                     # 7 standby
 );
 
 my @bitidx;
@@ -455,40 +437,15 @@
 #############################################################################
 
 my @chr = (
-   " ",
-   "\x{29eb}",
-   "\x{2592}",
-   "\x{2409}",
-   "\x{240c}",
-   "\x{240d}",
-   "\x{240a}",
-   "\x{00b0}",
-   "\x{00b1}",
-   "\x{2424}",
-   "\x{240b}",
-   "\x{2518}",
-   "\x{2510}",
-   "\x{250c}",
-   "\x{2514}",
-   "\x{253c}",
-   "\x{23ba}",
-   "\x{23bb}",
-   "\x{2500}",
-   "\x{23bc}",
-   "\x{23bd}",
-   "\x{251c}",
-   "\x{2524}",
-   "\x{2534}",
-   "\x{252c}",
-   "\x{2502}",
-   "\x{2264}",
-   "\x{2265}",
-   "\x{03c0}",
-   "\x{2260}",
-   "\x{00a3}",
-   "\x{00b7}",
+   " "       , "\x{29eb}", "\x{2592}", "\x{2409}",
+   "\x{240c}", "\x{240d}", "\x{240a}", "\x{00b0}",
+   "\x{00b1}", "\x{2424}", "\x{240b}", "\x{2518}",
+   "\x{2510}", "\x{250c}", "\x{2514}", "\x{253c}",
+   "\x{23ba}", "\x{23bb}", "\x{2500}", "\x{23bc}",
+   "\x{23bd}", "\x{251c}", "\x{2524}", "\x{2534}",
+   "\x{252c}", "\x{2502}", "\x{2264}", "\x{2265}",
+   "\x{03c0}", "\x{2260}", "\x{00a3}", "\x{00b7}",
    (map chr, 0x020 .. 0x7e),
-   "?",
 );
 
 utf8::encode $_ for @chr;
@@ -497,7 +454,7 @@
    my $i = 0x2000;
 
    my $scr = sprintf "\x1b[H--- KBD %08b CLK %d PC %04x RST %03b IFF %01b PUS %02x IM %03b\x1b[K\n", $KSTATUS, $CLK, $PC, $RST, $IFF, $PUSARTCMD, $INTMASK;
- 
+
    line:
    for my $y (0 .. 25) {
       $scr .= sprintf "%2d |", ++$y;
@@ -762,7 +719,7 @@
       #$INTPEND |= 2 if @PUSARTRECV && $XON; # VT102, 6.5 rxrdy
 
       # kick off vertical retrace form time to time
-      unless ($CLK & 0x3ff) {
+      unless ($CLK & 0x1ff) {
          $RST |= 4; # vertical retrace
       }