Vidicode Argus Basic Programmers Reference Manual

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
108
  
LEFT$    extract left part of a string 
LEFT$ extracts the specified number of characters from the left-hand side of a string.  The command: 
L$=LEFT$(ABCDEFGH,3)
will assign the string ABC to the string variable A$. 
 
The number of characters extracted must be between 0 and 255.  Attempts to extract more characters than exist in the string 
will return the entire string. 
Examples: 
Firstname$=LEFT$(Name$,6)
Da$=LEFT$(CLOCK$,2)
PRINT LEFT$(Now is the time for all good men.., 10)
Syntax: 
[string-var] = LEFT$ ( [string], [integer
0.255] )
See also: 
LEN, MID$, RIGHT$
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
109
  
LEN    get length of string 
LEN returns the length of the specified string, including spaces and non-printing characters. 
Examples: 
Size=LEN(Name$)
IF LEN(Name$) >30 THEN PRINT Name too long ..
PRINT LEN(Message$)
Syntax: 
[num-var] = LEN( [string] )
See also: 
LEFT$, MID$, RIGHT$
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
110
  
LENGTH    set or read serial port word length 
The LENGTH function is used to set or read the number of data bits used during serial data transfer. 
 
The number of bits used can be specified separately for each port, and may be set to 7 or 8 bits.  The most common format 
for ASCII systems is 8 data bits, no parity and 1 stop bit, which is the default format used by this modem.  This format must 
be used for sending data or machine language programs using the Xmodem protocol. 
 
If a user is connected to another terminal configuration, you might want to advise the other person that he will not be able to 
see what the application is expecting him to see, so it is very useful to read LENGTH at a certain stage in your program. 
 
After pressing the STOP button, the length for all ports will be configured to the default value of 8 bits. 
 
If no port is specified, the default output port as defined by OPORT is assumed. 
Examples: 
LENGTH 7
LENGTH#1,#2,#3,8
LENGTH#Port,Bits
IF LENGTH=7 GOSUB %WARNING
Syntax: 
LENGTH ( #[port] ) (, #...) [integer 5..8]
See also: 
BAUD, PARITY, SBITS
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
111
  
LINEFEED    enable/disable Line Feeds 
Most terminals and printers accept a combination of Carriage Return (ASCII 13) and Line Feed (ASCII 10) characters to 
indicate the end of a line, while others require only a Carriage Return, and insert a Line Feed automatically.  The 
LINEFEED command is used to switch Line Feeds on or off, as appropriate. 
 
LINEFEED ON causes the modem to insert a Line Feed after every Carriage Return in a transmitted data stream for the 
specified port. 
 
LINEFEED OFF disables transmission of Line Feeds for the specified port. 
 
If no port is specified, the default port as defined by OPORT will be assumed. 
 
With respect to the printer port (#7), there are two forms of the command that may be used: 
LINEFEED#7, ON/OFF
or 
PRINTER LINEFEED ON/OFF
There is a second syntax of LINEFEED. 
LINEFEED [num-var].
This command allows you to change the ASCII value of the linefeed character, which is normally set to the default value of 
10. 
Examples: 
LINEFEED ON
LINEFEED#2,#3,OFF
LINEFEED#7,ON
LINEFEED 10
Syntax: 
LINEFEED ( #[port] ) (, #...) ON/OFF
LINEFEED (=) [num]
See also: 
PRINTER
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
112
  
LINK    connect logical data streams 
LINK is used to create transparent links between two serial ports. 
The advantage of linking ports can be explained with the following example. 
 
Assume that a terminal is connected to port 1, and a computer to port 2, and that both are set for 9600 baud operation.  
There are various ways of connecting the two devices.  The first is to write a program that simply takes characters from each 
port and puts them to the other: 
10 BAUD#1,#2,12
20 REPEAT
30 PUT#2,KEY$#1
50 PUT$#1,KEY$#2
60 UNTIL FALSE
Unfortunately however, this short loop ties up the modem permanently, so that no other operation can be carried out.  
Furthermore, Argus BASIC, though fast, is not fast enough to keep up with two 9600 baud data streams, and software or 
hardware handshaking must be used to prevent loss of data. 
 
The alternative is to use the LINK command: 
10 BAUD#1,#2,12
20 LINK#1,#2
30 LINK#2,#1
40 REM - Remainder of program starts here
Here, the two LINK commands are used to establish a bi-directional, transparent link between ports 1 and 2.  Such a link 
will not interfere with the rest of the program, and will remain effective even when program execution ceases. 
 
You may ask whether it would be simpler to couple the terminal direct to the computer using an appropriate cable.  In this 
example that is probably the case, but there are situations where this is not practical; e.g. when the data format of the two 
devices is different.  With LINKed ports: 
•  the baud rate and data format of the linked devices need not be the same. 
•  it is possible to monitor the data flow and respond to specified character 
 sequences. 
•  data flow can be switched between different ports. 
•  incoming data can be routed to one or more output ports. 
Data monitoring carried out using the INPUT, GET, KEY and MATCH commands can be extremely useful, but will slow the 
link down.  A further command is therefore provided to enable handshaking over the link: 
HANDSHAKE LINK ON
This will prevent loss of data due to buffer overflow. 
HANDSHAKE LINK OFF
may be used to disable handshaking if speed is not likely to cause problems. 
 
The next example program uses the MATCH command to monitor the link for the string PASSWORD being received at port 
1: 
10 LINK#1,#2 
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
113
  
20 LINK#2,#1
30 HANDSHAKE#1 LINK ON
40 HANDSHAKE#2 LINK OFF
50 MATCH#1, PASSWORD
60 ...
Note that the first port number specified in the LINK command is that of the input port.  One or more output ports then 
follow: 
LINK#1,#2,#7
Here port 1 is the input port; ports 2 and 7 are outputs. 
 
The following will create a bi-directional link between ports 2 and 3 while allowing port 1 to monitor data received via port 2: 
LINK#2,#3,#1
LINK#3,#2
A port can also be linked to itself: 
LINK#1,#1
The effect of this is to provide character echo. 
 
If no port numbers are specified, the default input port defined by IPORT will be used as the input port, and the default 
output port defined by OPORT as the output port. 
 
The command: 
LINK OFF
may be used to disconnect linked ports.  Pressing RESET will clear the input and output buffers, and also terminate any 
existing links. 
 
Port 6 (keyboard and LCD display) can not be linked. 
Examples: 
LINK#1,#2
LINK PORT2,PORT7
LINK#1,#2,#3
LINK#In,#Out
LINK PORT8,PORT1
LINK OFF
Syntax: 
LINK ( #[port] (TO|,) (#[port] ) (, ...)
LINK OFF
See also: 
HANDSHAKE 
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
114
  
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
115
  
LIST    list BASIC program 
LIST is used to list the currently loaded program to the specified port. 
 
When used without a parameter, the entire program will be listed to the default output port as defined by OPORT. 
 
A range of line numbers can be specified; thus the following example will only list those lines from 500 to 1000 inclusive: 
LIST 500,1000
To list from the start of the program up to a specific line number, just omit the first parameter; e.g. to list all lines up to and 
including line 300 you would use: 
LIST , 300
Output is normally formatted so that: 
•  BASIC keywords are translated to upper case 
•  variable names have their first letter capitalized 
•  spaces are inserted to make programs more readable 
•  conditional commands such as IF, REPEAT, etc. are indented. 
The formatting feature can be enabled or disabled, using the commands 
LIST OFF and LIST ON respectively. 
 
There are a number of ways in which LIST can be used to obtain a printed copy of a program.  The first is to specify port 
number 7 which is the parallel printer port (assuming you have a printer attached): 
LIST#7
Alternatively, you may use the PRINTER ON command, followed by LIST. 
 
Yet another option is to set OPORT to 65 before printing. 
 
A very useful variant of LIST is the LIST AUTO command which is used for capturing programs that are going to be 
edited. 
Examples: 
LIST#7,500
LIST 70,150
LIST Label1 TO Label2
LIST OFF
Syntax: 
LIST ( #[port])(,#...) (line-num | label ( TO|, ) line- num |
label)LIST ON | OFF
See also: 
OPORT, PRINTER ON/OFF
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
116
  
LIST AUTO    list program for editing 
This is used to capture a special listed program for editing. 
 
This command lists programs without line numbers included.  Programs captured in this way can be edited offline and ASCII 
uploaded back to the modem using the AUTO command. 
 
When performing an ASCII upload to the modem, the AUTO command will automatically assign numbers to program lines. 
Syntax: 
LIST AUTO
See also: 
AUTO, LIST
  
						

							ARGUS Programmable Modem 
BASIC Programmers Reference Manual 
© 1990 - 1997 Vidicode Datacommunicatie BV 
117
  
LOAD    load BASIC program or data 
The principal use of LOAD is to copy programs from disk into program memory, at the location specified by the system 
variable PBOT. 
 
To load from the disk, use LOAD (followed by an optional exclamation mark) and the filename within double quotes: 
LOAD DIAL.PROG
By changing the value of PBOT it is possible to LOAD a number of programs into memory at once: 
LOAD Prog1
Base1=PBOT
PBOT=PTOP+2
Base2=PBOT
LOAD Prog2
By manipulating the value of PBOT one program can then call another.  Each program loaded in this way will have access to 
the same variables; i.e. the variable Name$ in one program will be the same in another, so that all variables are global. 
 
The second use of LOAD is to copy DATA from the disk to a certain address.  In this case you have to specify the address. 
Examples: 
LOAD Prog$
LOAD &4000, MODEM.PROG
LOAD &6800, Bytes$
LOAD !SETUP.PROG
LOAD FILE SETUP.PROG
Syntax: 
LOAD (!|FILE)(address)[string]
See also: 
RUN, SAVE