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1988-03-07
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SHOW87 Version 1.10
Copyright (c) 1987-1988 Eric Tauck
All Rights Reserved
03/06/1988
SHOW87 is a memory resident program that displays the entire state
of an installed 8087 coprocessor chip. This program will only
work if an 8087 is present. SHOW87 is very useful when debugging
code that contains 8087 instructions.
SHOW87 has two modes of installation. The default is the shell
mode in which SHOW87, rather than making itself truly resident,
executes a DOS shell. This allows you to deinstall SHOW87 by
typing EXIT at any DOS prompt. The disadvantage of the shell mode
is that a second command processor must be invoked, which uses an
extra 3000 to 4000 bytes of memory. The other type of
installation is the resident mode, which is specified by the /R
parameter. SHOW87 uses less memory in this mode, but cannot be
removed. SHOW87 alone uses about 5700 bytes of memory.
Once installed, the program may be invoked at any time by pressing
ALT-7. Invoking SHOW87 causes most of the upper half of the screen
to display the flags, registers, and other information regarding
the 8087. Pressing any key exits the display and restores the
screen. The normal sequence of events is to install SHOW87 before
debugging 8087 code and then removing SHOW87 when it is not needed
any longer.
If SHOW87 cannot properly install itself, it will display an error
message and terminate. The most common reasons for such an error
are insufficient memory and COMMAND.COM not found. COMMAND.COM is
only needed when SHOW87 is run in the shell mode. SHOW87 finds
the COMMAND.COM file by looking for the COMSPEC parameter in the
environment (see your DOS manual).
SHOW87 displays all 8087 information, including the instruction
pointer, the operand pointer, the operation code; the control,
status, and tag words; the precision, rounding, and infinity
control settings; the stack top; the condition codes and their
various interpretations; the exception settings and interrupt mask
settings; and the register values.
The condition code settings represent C3, C2, C1, and C0
respectively. The Comp, Test, and Exam fields display the meaning
of the condition codes as returned by the FCOM, FTST, and FXAM
instructions.
Register values are displayed in one of two ways. If the number
has a tag setting of VALID, the number is displayed in decimal
format. If the number has a tag setting of SPECIAL or EMPTY, a
hexadecimal dump of the number is displayed. After the mantissa
and exponent, the type of value (as interpreted by the FXAM
instruction) is displayed.