From: Anders Nordstrom (andersn@bcarsb82)
Date: Fri Aug 22 1997 - 08:54:55 PDT
Subject: BTF - BE27 - transition_pair
Behavioral Task Force - Errata Submission
Assigned Enhancement Request Number: BE27
Errata Name (Description): transition_pair
Section: 14.5.9
Date Submitted: 970701
Requestor: Paul Graham
Status: Submitted (priority not yet assigned)
Errors found in the Verilog LRM (IEEE 1364-1995).
Details:
The BNF for transition pair is:
transition_pair ::= 01 | 0x | 10 | 1x | x0 | x1
The BNF allows only lowercase x, which is odd, considering that both x and X
are allowed in output_symbol, level_symbol, and binary_digit.
There is also a sentence in the section:
Edge transitions involving z are treated the same way as edge
transitions involving x.
If the BNF is taken seriously, it is syntactically impossible to have an
edge transition involving z. Is the BNF incorrect, or does the quoted
sentence have no referent? I suspect that the BNF is incorrect. The
following syntax will work:
transition_pair ::=
01
| 10
| z_or_x zero_or_one
| zero_or_one z_or_x
zero_or_one ::= 0 | 1
z_or_x ::= x | X | z | Z
This allows both x and z, in lowercase and uppercase verions. This new
syntax may require a note saying that no whitespace is allowed between the
z_or_x and zero_or_one non-terminals.
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| Senior ASIC Designer |
| Northern Telecom Ltd. Email: andersn@nortel.ca |
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