AT&T PC6300 SUPPORT BBS - Bulletin Service

SUBJECT: GW-BASIC Notes for the PC6300
PROVIDED BY: AT&T PC-Hotline



DIFFERENCES BETWEEN IBM BASIC VERSION 1.1 AND GW-BASIC



1) IBM COMPATABILITY PACKAGE MODIFICATIONS

1.1) RESERVED WORDS AND TOKENS
The reserved words and tokens were incompatable,
making exchange of binary and protected program
files impossible. GW-Basic token values have been
modified by this modification package.

1.2) LINE PRINTER AND KEYBOARD OPEN MODE
IBM Basic allows these devices to be open without
a mode specification. GW-Basic would interpret
these cases as open for random and declare a mode
error.

1.3) RS232 SUPPORT
The /C switch on the IBM Basic command line allows
the user to specify the sieze of communications
buffers. This feature has been added to all
versions of Basic.

1.4) CLEAR Processing
CLEAR should turn off music, reset music to
foreground, turn off PEN and STRIG, and reset DRAW
scale color. Similar processing should happen for
LOAD, RUN, CHAIN, CLEAR, and NEW. This processing
has been added for all GW-Basic versions.

1.5) BSAVE and BLOAD
IBM Basic appends the .BAS suffix to file names
when the user does not supply a suffix. GW-Basic
did not append a suffix.

1.6) CENTER OF GRAPHICS SCREEN
IBM Basic calculates the center by dividing the
one relative screen dimensions by two. GW-Basic
calculates the center by dividing the zero
relative screen dimensions by two. The IBM Basic
method of calculating the center of the screen is
now used by GW-Basic.

1.7) COMMON STATEMENT
IBM Basic allows the user to define new variables
using the COMMON statement. GW-Basic declared an
error if a COMMON statement referred to a
previously undefined variable.

1.8) LIST STATEMENT
During PRINT and LIST processing, IBM Basic clears
characters from the end of the print item to the
end of line. All versions of BASIC now function in
this manner.

1.9) CURSOR DESIGN
A) The GW-Basic cursor is on only during character
input requests from the keyboard.
B) The IBM Basic displays different cursors for
the Screen Editor overstrike mode and insert
mode.
The GW-Basic cursor is now turned off when
printing characters to the screen. The cursor is
turned to the user cursor when the PRINT
statement terminates. When input is requested,
the cursor is turned to the insert mode cursor
or the overwrite mode cursor, depending on the
Screen Editor mode.

1.10) INKEY$, INPUT$, INPUT
A) INKEY$ did not return the same key codes as
IBM Basic
B) INPUT$ did not return the same key codes as
IBM Basic. It should be noted that IBM Basic
key codes returned to INKEY$ are not the same
as IBM Basic keycodes returned to INPUT$ for
all keys.
C) Device input from "KYBD:" read no break (no
interrupt takes place) if using the INPUT
statement. An interrupt took place if
INPUT$(N,kybd:) IS SPECIFIED.
GW-Basic now provides the OEM with filters for
mapping characters on input. These filters
provide the capability of returning IBM Basic
keycodes.

1.11) CHR$
Certain IBM character codes in the range
[&H00,&H1f] have been assigned fonts and are
printable. Other codes in this range have been
assigned functions (such as carriage return).
GW-Basic now provides filters which allow OEM to
decide which codes in this range are printable
and which specify control functions.

1.12) SCREEN function
SCREEN function requests for the character at the
current cursor position may return a zero in
place of &H20 (space) for IBM if there are no
non-space characters to the right of the
specified cursor position. GW-Basic can now
support this character code for the screen
function.

1.13) POKE/PEEK
Results of the POKE and PEEK statements were
different. The GW-Basic machine interface now
includes routines to filter PEEK and POKE
instructions. The OEM may now modify the PEEK or
POKE address and data value. Certain GW-Basic
routines have been provided for use in these
filters. GW-Basic provides the capability to
support the function of all PEEK and POKE
locations specified by IBM user documentation.

1.14) INITIALIZATION DIFFERENCES
A) HEADING: GW-Basic displays the heading when a
program is specified on the command line,
while IBM Basic does not print a heading or
display function keys in this case. The
GW-Basic machine interface now contains a
parameter that specifies to GW-Basic whether to
print the heading and function keys when a
program is specified on the command line.
B) FUNCTION KEY DISPLAY: GW-Basic did not give the
option of displaying the function keys when
BASIC initializes, when there is no program on
the command line. A configuration switch now
specifies the function key display switch
position on BASIC initialization.

1.15) ERROR CODES
Some of the error codes and messages were
different. GW-Basic error codes and messages have
been modified to conform to IBM Basic.


1.16) MUSIC AND SOUND
A) PLAY octave default not the same.
B) BEEP duration not the same
C) SOUND STATEMENT:
1)SOUND freq,0 causes the IBM Basic to be
flushed
2)GW-Basic does not perform range checking on
frequency.
3)SOUND statement foreground mode was not
interruptable by CTL-C or BREAK. This is a
problem because it is possible to create
extremely long notes.
These conditions are considered bugs and have
been fixed for all versions. Foreground SOUND
interruptability is available through a GW-Basic
keyboard routine provided to the OEM for use
within the speaker control support.

1.17) COLOR statement syntax
The IBM COLOR statement syntax was not
supportable by the GW-Basic OEM interface. This
problem has been fixed in GW-Basic.



2) DIFFERENCES WHICH WILL NOT BE RESOLVED

2.1) SCREEN EDITOR DIFFERENCES
(THESE DIFFERENCES MAY NOT EXIST IN SOME VERSIONS
OF GW-BASIC BECAUSE OF THE FLEXIBILITY OF THE OEM
INTERFACE FOR MAPPING AND OMITTING FEATURES)

A) Input sequences that wrap to a subsequent
physical line cause a scroll to open another
physical line. IBM Basic allows the user to
type over the text which is on the subsequent
line. The IBM Basic end of logical line is then
moved to the end of the logical line which is
being overwritten.
B) Skip-to-next-word function. When the cursor is
positioned on a space the IBM skip-to-next-word
control function will skip spaces until a word
is found, progress over the word and proceed to
the word following. The GW-Basic skip-to-next-
word control function will skip spaces until a
word is found.
C) TAB. In GW-Basic, after stopping at the last
position on a line, TAB will proceed to the
next line. IBM Basic TAB only operates on one
line.
D) Cursor movement control functions do not join
physical lines into logical lines. In IBM Basic
cursor movement can join lines.
E) Line delete. The GW-Basic Screen Editor uses a
character other than ESC for line delete.
F) GW-Basic extends logical lines to new physical
lines (when required by LF or wrapping at the
end of the screen). A new blank line is inserted
following the current line. When physical lines
following the first physical line in a logical
line are deleted, the line is removed from the
screen. In IBM Basic, lines are not inserted or
removed.
G) AUTO. The IBM AUTO statement allows the user to
modify the statement corresponding to the line
number printed by AUTO only. If the user uses
the Screen Editor to move to another line, or
otherwise attempts to modify the line number,
strange results are obtained. The GW-Basic AUTO
statement allows the user to modify any line by
making use of the Screen Editor to modify the
line number or to move to another line on the
screen.
H) Functions added to Screen Editor
1) HELP. This control function allows the
programmer to edit the last statement where
an error ocurred, or if no error ocurred,
the last direct statement.
2) DELETE WORD. This control function deletes
the current word starting at the current
cursor position, and ending at the character
previous to the next word
3) CLEAR TO END OF SCREEN. This control
function clears all data from the current
cursor position to the end of the screen.

2.2) Breaking from INPUT
IBM Basic allows the user to break from an INPUT
statement using either Control-C or BREAK. GW-Basic
provides only one BREAK function code. This
function code may be assigned to either BREAK,
Control-C, or both by the OEM. However, no special
processing is performed to differentiate between
the INPUT statement and other statements.

2.3) Sequences returned by the GW-Basic RANDOM NUMBER
GENERATOR (RND function) will NOT be identical to
sequences returned by the IBM Basic random number
generator.

2.4) /F and /S Options
IBM Basic statically allocates file space using
the /F and /S BASIC command line switches. GW-Basic
allocates space dynamically and is not limited by
these switches. GW-Basic will not declare an error
if the user specifies either of these switches.

2.5) File Format of BASIC
IBM Basic is in ".COM" file format. GW-Basic is in
".EXE" file format.

2.6) Fielded Strings
IBM Basic fielded strings retain their values
after the file is closed. In GW-Basic this space is
deallocated. Any field statement which is executed
while a file is opened, has no effect after that
file is closed. For example, assume file 1 is
opened, fielded, and closed. If file 1 is
reopened, it should be refielded.

2.7) VARPTR
In IBM Basic, the value returned by VARPTR for a
given file number is not subject to change during
program execution. In GW-Basic, FBD's are moved in
memory when files are opened and closed. To avoid
problems due to this difference, the statement
"X=VARPTR(file)" should be executed before every
referrence to X because a file buffer may be moved
in memory when another file is closed.

2.8) Line Printer Filenames
Line printer filenames have the following syntax:
"LPTn:[bin]"
Where if bin is included, the file is opened in
Binary mode. In this mode, tabs are not expanded
to spaces, and CR is not forced at end-of-line.

2.9) DATE$
Both IBM Basic and GW-Basic allow a single digit
for year. IBM Basic interprets the digit 8 as
1980. GW-Basic interprets the digit 8 as 2008.

2.10) Pen and Joy Stick
The statement 'STRIG ON' and 'STRIG OFF' perform
no function in GW-Basic. In IBM Basic these
functions are used to enable and disable the joy
stick trigger interrupts.

2.11) Parity Checking on the OPEN statement
There is an undocumented PE on the IBM OPEN
statement. This OPEN option enables/disables
parity checking on input. With no PE specified,
the IBM OPEN for communications will report no
parity errors.



3) IBM BASIC PROBLEMS FIXED IN GW-BASIC

3.1) Homing The Graphics and Text Cursor
IBM Basic does not home the cursor after CLS in
version A1.0. GW-Basic allows the OEM to choose
when to home the graphics cursor. The text cursor
is always returned home as per IBM PC Basic
version A1.1.

3.2) NAME statement On Open Files
IBM Basic allows the NAME statement to refer to an
open file. This causes no immediate problem, but
can lead to problems as in the following case:
10 OPEN"0",#1,"JUNK"
20 NAME"JUNK" AS "JUNK2"
30 KILL"JUNK2"
40 PRINT#1,"My data"
50 CLOSE
IBM Basic allows this program to execute. Data
printed to the file is lost. This is inconsistent
in that KILL is illegal when referring to an open
file.
GW-Basic and the standard MS-DOS version of
BASIC-86 do not allow NAME to refer to open files.

3.3) Detection Of Identical File Names
IBM Basic does not detect identical file names
when the only difference in the name is the case
of the alphabetic characters comprising the file
name. This problem prevents IBM Basic from
detecting that a file in an OPEN statement has
already been opened.
GW-Basic and the standard MS-DOS version of
BASIC-86 are able to detect this user error.

3.4) Interruptability Of Input From The Keyboard
Variable length input (INPUT n,var...) from
the keyboard is not interruptable using the break
key. The program:
10 OPEN "KYBD:" FOR INPUT AS 1
20 INPUT #1,A$
30 GOTO 20
will read break as a character (the program is
virtually uninterruptable). This problem is fixed
in GW-Basic.

3.5) Communications
1) End Of File. IBM-PC Basic returns EOF true
whenever the input buffer is empty. GW-Basic
returns EOF true only when file was opened in
non binary mode, and CTL-Z has been received.
Once EOF is true, it remains true until the
file is closed. This is more analogous to the
way EOF works on other devices.
2) Default Data Bits. IBM Basic documentation
states that the default bit count for
communications is 7. The commas in the
statement:
OPEN "COM1:,,,"
cause 7 bit mode to be invoked. However, if
parity or speed are specified, the default data
bit count is set to 8. GW-Basic defaults to 7
data bits.

3.6) Graphics
1) POINT. The IBM BASIC POINT function does not
detect that certain coordinates are not on the
screen and therefore are not legal.
2) GET and PUT. The array format and speed
capability of these statements is supportable
by GW-Basic. However, the operation of these
commands is highly dependent on hardware design
and the implementation of OEM specific
routines.

3.7) Screen Editor
1) The IBM Screen Editor returns a zero to input$
function when a null function key is depressed.
GW-Basic Screen Editor returns no key code to
INPUT$ for null function keys.
2) The IBM Screen Editor terminates function key
expansion when a key code greater than &H7f is
encountered. The high bit of this key code is
removed. GW-Basic allows codes greater than
&H7f. In late ROMs, the IBM Screen Editor will
not remove the high order bit from codes
returned by function key expansion.

3.8) Trailing Blanks
The following BASIC program demonstrates a problem
in IBM Basic:
10 OPEN "JUNK FOR OUTPUT AS #1
20 PRINT #1,"ABC "
30 CLOSE #1
40 OPEN "JUNK" FOR INPUT AS #1
50 INPUT A$
60 PRINT LEN(A$)
70 CLOSE #1
The IBM Basic result of the print statement in
line 60 is 13. The trailing blanks have not been
removed. GW-Basic removes these trailing blanks as
specified by the ANSI Standard.



4) RS232 COMMUNICATIONS

Previous releases of GW-Basic were incompatable with
IBM-PC Basic communications in the following areas:
1) When a com file was opened with default
parameters and closed, a CONTROL-Z (1A hex) was
sent to let the other end of the RS-232
protocol know that end-of-file had been
reached. This is not done in IBM-PC BASIC.
2) Under GW-Basic if a COM device was opened with
the BIN option, EOF always returned false. In
ASCII mode, EOF returned false until it
received a CONTROL-Z, after which time it
always returned true.
These changes made EOF behave in a device independent
manner. For example, a program which was written to
read sequentially through a disk file, stopping when
EOF was true, can now be used to read a COM file. For
another example, GW-Basic can load "COM1:" and terminate
when the load is finished if the user on the other end
of the RS232 line types SAVE "COM1:",A.

The number of application programs which have been
written to use IBM-PC COM cannot be ignored. The
following change in GW-Basic is intended to provide
compatability with IBM-PC Basic while retaining the
features added to GW-Basic.
NOTE: This change is isolated to version independent
code and has no effect on OEM written routines.

COM files can be opened in one of the following ways:

1) With the ASC option
In this mode, EOF is always false until a CTL-Z
is received. When a file is opened for OUTPUT
or RANDOM, a CTL-Z is sent when the file is
closed.

2) With the BIN option
In this "raw" mode, Basic performs no filtering
of data. This includes forcing carriage return
when line width is exceeded. This option
overrides the LF option. EOF has the same
meaning as it does in IBM-PC Basic. EOF is TRUE
if no data exists in the input buffer.

3) With neither the BIN nor the ASC options.
This mode is compatible with IBM-PC Basic. No
CTL-Z is sent when the file is closed. EOF is
TRUE if no data exists in the input buffer.

BSAVE, BLOAD force the mode to BINARY. This insures
BASIC will not force any Carriage Returns if the device
is not 255 (infinite).

SAVE "COMn:...",A forces the mode to ASCII.

LOAD 'COMn:..." forces the mode to ASCII if the first
character received is less than 80 hex, indicating an
ASCII file is being loaded. This ensures that ASCII
LOADs will terminate.

COM file syntax:
"COMn: [speed] [,parity] [,data] [,stop] [,RS]
[,CS[n]] [DS[n]] [,CD[n]] [,LF] [,ASC] [,BIN]"
Where:
SPEED baud rate in bits per second
PARITY N, E, 0 (none, even, odd)
DATA 5,6,7,8 bits per byte
STOP 1, 1.5, 2 stop bits
Default for baud greater than 110 is 1
Default for 110 baud or lower & 5 data bits
is 1.5
Default for 110 baud or lower & 6-8 data bits
is 2
RS Suppress RTS (Request To Send)
CS[n] Controls CTS (Clear To Send)
DS[n] Controls DSR (Data Set Ready)
CD[n] Controls CD (Carrier Detect)
This is also referred to as RLSD
(Receive line Signal Detect)
LF Send a Line Feed character (X'OA')
following a Carriage Return (X'OD')
ASC Open COM file in ASCII mode
BIN Open COM file in BINARY mode

The RTS (Request To Send) line is turned on when you
execute an OPEN "COM..." statement unless you include
the RS option.
If CD is omitted, it defaults to CSO
If DS is omitted, it defaults to DS1000
If CS is omitted, it defaults to CS1000
If RS is specified and CS is omitted, then CS defaults
to 0.

Normally I/O statements to a communication file will
fail if the CTS (Clear To Send) or DSR (Data Set Ready)
lines are not cabled. The CS and DS options allow you
to avoid this problem by ignoring these lines. If the
[n] argument is included, it specifies the number of
milliseconds to wait for the signal before returning a
"Device Timeout" error.

If the argument [n] in the CS, DS, and CD options is
omitted, or equal to 0, then that line's status is not
checked at all.

NOTE: The speed, parity, data, and stop parameters are
positional, but RS, CS< DS, and CD may appear in any
order after STOP.

When included in the parameter list, LF will cause a
Line Feed to be sent after a Carriage Return.