Hardware Reference
In-Depth Information
Program text
Processor
with
Stack
registers
Source file
Subroutine
call stack
Interpreter
commands
Error output field
Input field
Output field
Values of global variables
Data segment
Figure C-10.
The tracer's windows.
The upper left window is the processor window, which displays the general
registers in decimal notation and the other registers in hexadecimal. Since the
numerical value of the program counter is not very instructive, the position in the
program source code with respect to the previous global label is supplied on the
line below it. Above the program counter field, five condition codes are shown.
Overflow is indicated by a ''v'', the direction flag by ''>'' for increasing and by
''<'' for decreasing. The sign flag is either ''n'', for negative or ''p'' for zero and
positive. The zero flag is ''z'' if set, and the carry flag set is ''c''. A ''
−
'' indicates
a cleared flag.
The upper middle window is used for the stack, displayed in hexadecimal. The
stack pointer position is indicated with an arrow =>''. Return addresses of subrou-
tines are indicated by a digit in front of the hexadecimal value. The upper right
window displays a part of the source file in the neighborhood of the next instruc-
tion to be executed.
The position of the program counter is also indicated by an
arrow ''=>''.
In the window under the processor, the most recent source code subroutine call
positions are displayed. Directly under it is the tracer command window, which
has the previously-issued command on top and the command cursor on the bottom.
Note that every command needs to be followed by a carriage return (labeled Enter
on PC keyboards).
The bottom window can contain six items of global data memory. Every item
starts with a position relative to some label, followed by the absolute position in
the data segment. Next comes a colon, then eight bytes in hexadecimal. The next
11 positions are reserved for characters, followed by four decimal word representa-
tions.
The bytes, the characters, and the words each represent the same memory
