QBasic Serial Port Control

[DigiTan]

I'm a doing a PC interface project that involves having a AVR µcontroller connected to the COM1 port through one of those TLL/RS-232 converter chips (MAX232A). The electronics are looking nice; now I have to figure out to transfer stuff to and from this AVR.

Basically, I want to use the AVR's built-in UART. It's got 8 bits, no parity, 1 stop bit, and I'll probably have it run at 9600bps.

I'm in the process of (re)leaning QBasic just for this project (and maybe for later, but I won't go into that). I need to know how to get and send bytes using my COM1 port, so my questions boiled down to:

How do I declare the baud rate in QBasic?
It think this involves the "OPEN" command, because I could not get a lot of details on it. The tutorials and source code use it, but don't really explain the syntax of this instruction. Also, what other preferences are set by the OPEN command?

How do I send and receive?
To transfer data 1 byte at a time, exactly what syntax should I use? And what COM port pins are involved in this process?

What happens when the program detects incoming COM1 data?
I read somewhere that QBasic is able to jump into an interrupt when serial data arrives. This would be extremely helpful, because it'd prefer to use an interrupt rather that poll the port constantly.

What pins need to be used?
Most interface circuits on seem to need the "Receive Data," "Transmit Data," and "ground" pins. Would I ever need the other others like "Clear To Send," "Data Terminal Ready," etc? I'm guessing these are used to avoid collisions?

 

[csaba911]

I have not used QBasic for at least 10 year.
This is my best gues !!!

How do I declare the baud rate in QBasic?

OPEN "COM1:9600,N,8,1,BIN" FOR OUTPUT AS #1

OK
I must asume you dont have this help available to you !?
Just pullend of from qbhelp, hope you can use it.

Opens and initializes a communications channel for I/O. The OPEN COM
statement must be executed before a device can be used for communication
using an RS232 interface.

Optimization Note
■ If there is not an OPEN COM statement in your program, you can
reduce the size of the .EXE file by linking with the stub file
NOCOM.OBJ.

OPEN "COMn: optlist1 optlist2" [FOR mode] AS [#]filenum% [LEN=reclen%]
■ If there are syntax errors in the OPEN COM statement, BASIC generates
the error message, "Bad file name."
■ The argument filenum% is the number used to open the file.
■ The OPEN COM statement has many options, which can be separated into
two option lists:
- optlist1 contains the most general and often-used parameters;
- optlist2 contains options used in special situations.
■ optlist1 specifies the communication line parameters and
has the following syntax:

[speed] [,[parity] [,[data] [,[stop]]]]

■ Following are the valid values for optlist1 options:

Option Description Range (default in bold)
═══════ ══════════════════════════════ ═══════════════════════════
speed Baud rate (bits per second) 75, 110, 150, 300, 600,
1200, 1800, 2400, 9600
parity Method of parity checking N, E, O, S, M, PE
(none, even, odd, space,
mark, error checking)
data Number of data bits per byte 5, 6, 7, or 8
stop Number of stop bits 1, 1.5, or 2(1)
──────────────────────────────────────────────────────────────────────
(1) The default value is 1 for baud rates greater than 110. For
baud rates less than or equal to 110, the default value is
1.5 when data is 5; otherwise, the value is 2.

■ Options in this list must be entered in the order shown. Use
comma placeholders for defaults. For example,
OPEN "COM1: ,N,8," FOR INPUT AS #1

■ Only the baud rates shown are supported. Any other value for speed
is invalid.
■ The PE parity value turns on error checking for parity errors.
■ If you set data to eight bits per byte, you must specify no
parity (N).

Important
■ Because BASIC uses complete bytes (8 bits) for numbers, you must
specify 8 data bits when transmitting or receiving numeric data.
■ If any options from optlist2 are chosen, comma placeholders must
still be used even if all of the optlist1 options are defaults.
For example:

OPEN "COM1: ,,,,CD1500" FOR INPUT AS #1

■ The optlist2 options can be specified in any order, and must
be separated from one another by commas. There are three types
of options: data mode, buffer size, and handshaking.
■ The data-mode options (ASC, BIN, and LF):

Option Description Default
══════ ═════════════════════════════════════════ ════════
ASC or Specifies treatment of tabs, carriage BIN
BIN returns, and Ctrl+Z in the data stream:

ASC BIN
═══ ═══
Tabs expanded to blanks Yes No
CR forced at end of line Yes No
Ctrl+Z means end-of-file Yes No
Ctrl+Z sent when device closed Yes No

LF Effective only with the ASC option. Ignored
Used to enable communication files (as part
to be printed on a serial line printer. of BIN
Causes a LF character (0AH) to be default)
automatically sent after each CR (0DH).

Note that the carriage return may be sent as
a result of the width setting for the device.
Note also that INPUT and LINE INPUT, when used
from a COM file that was opened with the LF
option, ignore the line feed.

■ The buffer-size options for sequential modes (RB and TB):

Option Description
══════ ══════════════════════════════════════════════════════
RB[n] Receive buffer size (in bytes)

If the RB option is not used or n is omitted, the
default is 512 bytes, unless overridden by the /C option
in the BC or QBX command line. Maximum receive buffer size
is 32,767 bytes.

TB[n] Transmit buffer size (in bytes)

If the TB option is not used or n is omitted, the
default is 512 bytes.

■ Handshake and timing options (RS, CD, CS, DS, and OP):
Option Description
══════ ══════════════════════════════════════════════════════
RS Suppresses detection of Request To Send (RTS).

CD[m] Specifies the timeout period on the Data Carrier Detect
line (DCD). If no signal appears on the DCD line (the
DCD line remains low) for more than m milliseconds, a
device timeout occurs. If a CD timeout occurs, ERDEV
contains 130 (82H).

Default if CD option not used,
m is omitted, or m = 0 Range, if m specified
────────────────────────────── ───────────────────────
m = 0, which means ignore the 0 - 65,535 milliseconds
state of the DCD line.

CS[m] Specifies the timeout period on the Clear To Send line
(CTS). If no signal appears on the CTS line (the CTS
line remains low) for more than m milliseconds, a device
timeout occurs. If a CS timeout occurs, ERDEV contains
128 (80H).
Default if CS option not used
or m is omitted Range, if m specified
────────────────────────────── ───────────────────────
m = 1000 milliseconds 0 - 65,535 milliseconds
(m = 0 means ignore the
state of the CTS line)


DS[m] Specifies the timeout period on the Data Set Ready line
(DSR). If no signal appears on the DSR line (the DSR line
remains low) for more than m milliseconds, a device
timeout occurs. If a DS timeout occurs, ERDEV contains
129 (81H).

Default if DS option not used
or m is omitted Range, if m specified
────────────────────────────── ───────────────────────
m = 1000 milliseconds 0 - 65,535 milliseconds
(m = 0 means ignore the
state of the DSR line)

OP[m] Specifies how long the OPEN statement waits
for all communications lines to become active:

Default if
Default if OP OP used, but
not used m omitted Range, if m specified
─────────────────── ────────── ───────────────────────
10 times the CD or 10 seconds 0 - 65,535 milliseconds
DS timeout value,
whichever is greater

Usage Notes
■ Specifying the argument reclen% is effective only in random-access
mode. You can use any of the random-access I/O statements, such as
GET and PUT, to treat the device as if it were a random-access
file.
■ Use a relatively large value for the OP option compared to the CS,
DS, or CD options.
■ The argument mode is one of the following string expressions:

Mode Description
══════ ═════════════════════════════════
OUTPUT Specifies sequential output mode.
INPUT Specifies sequential input mode.
RANDOM Specifies random-access mode.

If mode is omitted, it is assumed to be random-access input/output.

■ The OPEN COM statement performs the following steps in opening a
communications device:
1. The communications buffers are allocated and interrupts are
enabled.
2. The Data Terminal Ready line (DTR) is set high.
3. If either of the OP or DS options is nonzero, the statement waits
for the timeout period for the Data Set Ready line (DSR) to go
high. If a timeout occurs, the process goes to step 6.
4. If the RS option is not specified, the Request To Send line
(RTS) is set high.
5. If either of the OP or CD options is nonzero, the statement waits
for the timeout period for the Data Carrier Detect line (DCD)
to go high. If a timeout occurs, the process goes to step 6.
Otherwise, the RS232 device has been successfully opened.
6. If there is a timeout, the open fails. The process deallocates
the buffers, disables interrupts, clears all of the control
lines, and generates the message, "Device timeout." In addition,
for DOS, the process sets the value of ERDEV$ to COM and sets ERDEV
to a value that indicates the signal line that timed out, according
to the following table:

ERDEV value Signal line
═══════════ ═════════════════════════════════
128 (80H) Clear to Send (CTS) timeout
129 (81H) Data Set Ready (DSR) timeout
130 (82H) Data Carrier Detect (DCD) timeout

Csaba911[/b]

 

[DigiTan]

Okay, that should give me a really good basis to start on. That description was very detailed. Where'd you find it? 8)

 

[csaba911]

Just press ALT and H for HELP or Shift+F1 !?


Here is some Qbasic fanatic page.
**broken link removed**
You can download qb7.1

I have not download it or tested it myself.


csaba911