This procedure physically connects a serial printer to the local system via a COM port, and defines the printer’s method of handshaking (defined below).
Following the manufacturer’s instructions for system and printer power settings and connection, connect the printer to the system with proper cabling.
Once the printer is properly connected to the system, turn on the system and the printer according to manufacturer-supplied instructions.
Start Windows.
Start an mvTerm session within mvBase.
Log to the SYSPROG account.
Choose and implement a method for handshaking according to the three options listed below.
The computer can transmit characters faster than most printers can mechanically print them. This creates the need for handshaking signals to be sent back and forth between the computer and the printer. Handshaking allows the printer to tell the computer when to stop sending data and when to commence sending data again.
DTR (Data Terminal Ready)
This handshaking technique allows the printer to raise or lower a control signal, called a Data Terminal Ready signal, when its buffer is nearly full. According to RS232 convention, when DTR is high, the computer can send data; when DTR is low, the computer cannot send data until the signal goes high again. In some cases this convention is reversed; most printers, however, can be switched to work in either manner.
The DTR technique is the most common method used, since most printers have DTR control. It should not be used, however, if the printer is connected to a phone line, since the modem that controls the phone line reacts to DTR signals. Use the X-ON/X-OFF handshaking technique if your printer is connected to a modem.
X-ON/X-OFF
With this handshaking technique, the printer actually sends a character to the computer (X-OFF) that halts data transmission, then later sends another character (X-ON) that starts data transmission again. The X-OFF character is DC3(X’13’), the X-ON character is DC1(X’11’).
Padding
Buffering was the first attempt at flow control; that is, the printer itself would store a certain number of characters in a buffer until it could print them. At higher baud rates, buffering is not sufficient for this method because certain characters such as line-feed, carriage return, and form-feed take more time to process than do other characters.
Thus, in this technique, the programmer inserts null codes. On the mvBase system, this can be done by changing the line-feed and form-feed delay with the TERM command.
Because every printer has unique timing requirements, it is necessary to experiment in order to determine the right combination for each printer. With enough time and experimentation, this method should work for any printer.
The primary drawback to this handshaking technique is the time required to experiment with the optimal settings for each printer.
Once the serial printer is physically connected to the system and you have successfully defined the handshaking method, perform the next procedure, Defining Communications Protocols for the Serial Printer.
See Also
Setting Up mvBase Printers on COM Ports