Cre Operating Considerations - RCA CDPl8S693 User Manual

User Manual for Microboard Computer Development System CDP18S693 & CDP18S694
18
CREATE SOURCE FILE
USING EDITOR
l i l t
FIX "T R IV IA L " ERRORS (RE) ASSEMBLE
USING EDITOR ANY ERROR DIAGNOSTICS?
•YES---------- NO
l
RUN
ANY BUGS?
I
PROGRAM WORKS
Fig. 4—Flow chart for "bug-free" program.
A source program may be viewed as a long sequence
of characters. When the COSMAC Resident Editor
reads the source file, it places this character sequence in
memory, with the code in each memory byte
representing one source program character. The user is
then free to type commands to the Editor to
m anipulate the memory representation of the
program. For example, the user may identify a specific
location and specify a character sequence to be
inserted there. He may also identify certain characters
to be deleted or altered. He may ask the Editor to
search for the occurrence of specific character
sequences, after which further memory modifications
(corrections) may be made. (Details of available
commands are given later).
After he is satisfied that the new memory
representation of the file contains all the desired
changes (frequently the user begins an editing session
with a hand-written list of the changes to be made), he
asks the Editor to write (create) a new file containing
the new version of the program. This new file is then
used as the input file for a reassembly.
CRE Operating
Considerations
Memory Space Requirements
CRE requires about l00 bytes of the RAM work
space for its own internal purposes. The remainder of
the available RAM space is used as an editing area
called a buffer. Virtually all CRE operations involve
the buffer. CRE is designed to take advantage of all of
the available RAM space for its buffer area.
All but the l00 bytes of work space are available for
this purpose in the 4 kilobytes of RAM supplied. If
more RAM is present in the system, CRE will
automatically add it to its buffer area. It tests for
additional RAM the same way CRA does.
I
FIX LOGICAL ERRORS
Input and Output Files
USING EDITOR
the buffer from the I/O terminal keyboard and then
causing CRE to write this information onto an output
tape (which will contain the created file).
reading portions of it into the buffer, then using CRE
commands to alter the contents of the buffer, and
finally writing the results onto the output file.
Typically, the output file is a new version of the input
file. After an editing session, the new version is
retained and the old version is discarded (although it
9 2 C S - 2 8 I 9 8
may be temporarily saved for future reference or
backup).
buffer, means to examine and modify the contents of
the buffer in many ways, and means to write the buffer
contents onto an output file. Alternatively, when an
input file does not exist, the user creates an output file
by loading the buffer from the keyboard.
Record Formats
CRE is designed to execute, it is fundamentally
important that the user understand how information is
normally recorded on the I/O media (tapes) and in the
buffer.
consists of a sequence of characters. The length of a
line is restricted to 78 or fewer characters of data. Thus,
a line in a file is normally printable as a line on the 1/ O
terminal printer. Each character is represented by an 8-
bit code or byte, either on the tape or in memory.
Typically, every character in a line is a printable
character (including space or blank). Every non­
either by hitting an appropriately marked key (e.g.,
Normally, a user creates a file using CRE by filling
An existing (input) file may be modified (edited) by
Thus CRE has means to read an input file into the
In order to understand the various commands which
A file is a sequence of records or lines. Each line
printing character code represents a control character.
A control code may be generated on the keyboard
RETURN, ESC, etc.) or by depression of the CTRL
button while hitting another key. The printer reacts to
the receipt of a control character in one of several
possible ways. Some control characters (such as
carriage return, line feed, bell, etc.) cause the printer to
execute a specific control function. Other control
codes either are ignored by the printer or may cause the
equivalent of a space on the printed line.
A line in a file may contain control characters (with
certain restrictions to be discussed later). If it does, it is
quite possible that its printed record will not
completely reflect the true contents of the line. CRE
treats most control characters which it encounters
within a line in the same manner as it treats printing
characters. However, certain control characters have
special meaning to CRE.