#! perl
use strict;
use warnings;

my $orig = 0b10100111_00010000;
my $text = error_state('E') + (mode_and_status(7, 'B', 1) << 8);

die "$orig != $text: $!" unless $orig == $text;

my $msg    = pack  ('n', $text);
my $decode = unpack('n', $msg);

print "text:   >$text<\n";
print "msg:    >$msg<\n";
print "decode: >$decode<\n";

die "$decode != $text: $!" unless $decode == $text;

sub error_state
{
    my ($error_type) = @_;
    my  $shift_count = ord($error_type) - ord('A');

    return 1 << $shift_count;
}

sub mode_and_status
{
    my ($mode, $status, $additional_status) = @_;
    my  $status_shift = ord($status) - ord('A');

    return $mode + (1 << $status_shift + 4) + ($additional_status << 7
+);
}
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(Error handling has been left as the proverbial exercise for the reader!)