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SEMI M13-1103 © SEMI 1988, 2003 5 ma x mi n Figure 4 Field Location for Notched Wafers

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SEMI M13-1103 © SEMI 1988, 2003 4
Figure 3
Code Field Location for Flatted Wafers
SEMI M13-1103 © SEMI 1988, 2003 5
max
min
Figure 4
Field Location for Notched Wafers
SEMI M13-1103 © SEMI 1988, 2003 6
Figure 5
Character Skew
NOTE: This line is parallel to the bottom of the code field
window.
R
adj
Figure 6
Adjacent Character Misalignment
R
line
Figure 7
Line Character Misalignment
7 Alphanumeric Error-Detecting Method
7.1 The alphanumeric check characters in character
locations 17 and 18 are a required part of the Code
defined in this specification.
7.2 All single-character substitution errors are detected.
7.3 All two-character transposition errors are detected
for any message up to 58 characters in length.
7.4 The character set may be expanded into the first 59
characters of the ASCII 64-character set.
7.5 There exist simple recursive algorithms for error
detection and check character generation that do not
require the use of multiplication or division.
7.6 Definition of the Error-Detecting Method
7.6.1 For the purpose of describing the error-detecting
method, we define the following symbols:
• A
i
represents the i
th
ASCII character.
• a
i
represents the numerical value assigned to A
i
.
7.6.2 The characters are numbered from left to right,
so that the message is given by
A
1
A
2
A
3
...A
18
.
7.6.3 A complete description of the error-detecting
method is given by the following seven rules:
7.6.3.1 The numerical value a
i
is found by subtracting
32 from the ASCII decimal representation of A
i
(refer
to Table 4).
7.6.3.2 An ASCII character A
i
is allowed only if its
numerical value a
i
is one of
0,1, 2,...,58.
7.6.3.3 The check character A
17
must be one of the
ASCII characters A,B,C,D,E,F,G,H.
7.6.3.4 The check character A
18
must be one of the
ASCII characters 0,1,2,3,4,5,6,7.
7.6.3.5 The check character pair A
17
A
18
may not be
one of the combinations H3, H4, H5, H6, H7.
7.6.3.6 When the message is written, the check
characters A
17
and A
18
are chosen such that 59 divides
the expression
8
17
a
1
+ 8
16
a
2
... + 8
2
a
16
+ 8a
17
+ a
18
without a remainder.
7.6.3.7 If, on reading the message, 59 does not evenly
divide the expression given above, an error has
occurred.
7.7 Suggestions for Implementation — The error-
detecting method can be implemented directly by
calculating the expression given above, and the check
characters can be found by exhaustive search. However,
this approach is unnecessarily complex; a decrease in
complexity can be made by taking advantage of three
simple observations.
7.7.1 First, since we are interested only in the remain-
der of the final expression after dividing it by 59, we
can avoid working with large numbers by subtracting
59 repeatedly after each operation until the result is less
than 59.