| Published By | Date | Version | Knowledge Level | Keywords |
|---|---|---|---|---|
| Revelation Technologies | 14 NOV 1989 | 2.X | EXPERT | V124 |
V124 provides facilities for low level access to an asynchronous communications port.
V124(operator, device.var, buffer, bytes, status)
By using V124, data may be read from or written to a port, and communication settings may be altered, although this is more easily accomplished using the system subroutine V123. For MS-DOS, the device driver COMMDVR.IBM must be an assigned device in the CONFIG.SYS file (see the TCL command TERMINAL). For OS/2, the device driver can be either COM01.SYS or COM02.SYS.
Use operator to pass a literal value indicating the operation to perform. The following is a list of the operators available:
| Operator | Operation |
|---|---|
| OP | Opens a port to device.var. This should always be preceded by an R/BASIC FLUSH operation. |
| CL | Closes the port associated with device.var. An opened port must be closed to avoid subsequent corruption of files. |
| CI | Control In. Reads the current settings for the port (see CO below for a description of these settings). |
| CO | Control Out. Sets the communication parameters for the port (see the system subroutine V123 for further information regarding these parameters). This must be a string of seven ASCII characters (7 bytes) passed in buffer and specifying the new settings. The format is as follows: Byte # - Description 1 - An ASCII character (not an integer) specifying the baud rate code. The codes are as follows: Code - Baud rate 1 - 50 2 - 75 3 - 110 4 - 134.5 5 - 150 6 - 200 7 - 300 8 - 600 9 - 1200 10 - 1800 11 - 2000 12 - 2400 13 - 3600 14 - 4800 15 - 9600 16 - 19200 2 - An ASCII character (not an integer) indicating the number of stop bits 3 - An ASCII character (not an integer) indicating the number of data bits 4- A literal character indicating the parity mode 5 & 6 - Protocol. This is two bytes in length, and requires setting bits 4 and 16. Bit 4 indicates XOFF mode if set. Bit 16 indicates STRIP mode if set. 7 - An ASCII character (not an integer) indicating the break count |
| RD | Read. Data is read from buffer. V124 does not wait for a [CRLF], but reads whatever data is in the buffer. |
| WR | Write. The data specified in buffer is written to the port. |
| TB | Test Break. If the break key is pressed, a break signal is sent to the port. |
Use device.var in an OP operation to return the DOS internal variable for the device driver. This variable is used by subsequent V124 operators.
Use buffer to pass the DOS internal name for the communications port to access when opening device.var; or, in the case of a CI or WR specified operator, the data to write to the port. The ASCII character 0 must be appended to the DOS internal name specified (as a terminator).
Use bytes to pass the number of bytes required for the operation. This parameter is used only with a CI operator.
V124 returns false in status if the operation is successful, or true if not. This parameter is used only with an OP or CI operator.
If operator is CI or RD, the data is passed in buffer. If operator is CI or OP, status returns true if the operation is successful and false if not.
* The following code demonstrates the use of V124
DECLARE SUBROUTINE V123, V124, MSG
DECLARE FUNCTION FUNCTION.KEY
device.var = ""
buffer = "COMM$":CHAR(0)
bytes = ""
status = ""
* Flush buffers and open the port
FLUSH
V124("OP", device.var, buffer, "", status)
IF status THEN
MSG("Unable to open the device","","","")
STOP
END
* A simple terminal emulator
MSG("Initializing terminal emulation mode","","","")
stop.key = FUNCTION.KEY("F9") ;* exit key
*Input loop, alternately checking input buffer and keyboard
buffer = ""
LOOP UNTIL buffer = stop.key
V124("RD", device.var, buffer) ;* check buffer
PRINT buffer: ;* echo to screen
V124("TB" ,buffer) ;* test for break key
;* get keyboard input and echo to screen
IF buffer NE stop.key THEN
* Write keyboard input to buffer
V124("WR", device.var, buffer)
END
REPEAT
V124("CL", device.var) ;* close port
MSG("Ending terminal emulation","","","")
STOP