Data Printer

Truman tells about his effort to Interface the Integral Data IP-125 printer to the TRS80 with a minimum of fuss. The manu-Truman Krumholz script he submitted was printed on the IP-125, using the TEXT80

Springfield Mo ,exl described in our Jan-Feb 79 Issue. The IP-125

Is available from several sources (check our advertisers!) for about $800.00.

I am using an Integral Data IP-125 printer with my TRS80. Mine has one option, the printer control, which costs an additional $39.00. I would strongly recommend this option for use with the TRS80. since it Includes an automatic line feed which is lacking on the TRS80tAlso, with this option there are four different print densities (under software control) and the ability to enhance characters. It also includes the ability to select and deselect the printer (also under software control).

The IP-125 requires a four microsecond or wider strobe pulse. The TRS80 parallel printer port provides a 1.6 microsecond strobe pulse. The IP-125 acknowledge signal is low when busy whereas the TRS80 busy terminal must be high when busy. These two signals are not compatible Also, some way must be found to achieve proper timing of the acknowledge signal from the printer.

The way I did this, was to generate a sort of artificial busy signal after each character is sent to the printer. If this Is not done the printer omits characters and finally hangs up. This method slows down the transfer of data, making the timing much less critical. The transfer rate Is still faster than a 2400 baud Interface.

One half of a 74LS123 one shot is used to make the strobe pulse for the printer (see Fig. 1) The TRS80 strobe pulse is fed to the one shot and the output pulse, now five microseconds wide. Is used for the printer strobe pulse. This strobe pulse is also fed to the other half of the 74LS123. This one shot is triggered by the trailing edge of the strobe pulse. The timing of this one shot generates an output pulse ap proximately three milliseconds wide. This is the artificial "busy" signal. It is low when busy and high when not busy. The printer acknowledge signal has the same polarity These two signals are fed to a two input nand gate (74LS00). BothJj signals must be high (not busy), for the output of^ the gate to be low. This low is the "not busy" signal for the TRS80.

All data lines are fed directly. The five volts for the Interface is obtained from the printer (Pin 25). A piece of perf board one and one-half inches square provides space for the interface. It is located at the printer end of a five foot cable.

There are a few things to remember for anyone using the interface described here. There are no "OUT PAPER" or "FAULT" signals provided by the printer. OUT PAPER on the TRS80 Is pulled low by this Interface. FAULT is made high by the TRS80. I did not provide a "printer on" signal to the TRS80; it thinks the printer is turned on. even when it isn't. This could easily be changed by using the printer five volts as control. I chose not to do this. If you POKE the printer driver address Into the display driver as described In 80—US No 2. then you should use the printer's smallest print. The reason for this Is that control code 31 is the printer code for the smallest character (16.5 CPI). If you are using larger characters, a CLS In the program will change the print to the smallest size. Any programs written for a printer will function normally.

I am very happy with the IP-125. I particularly^ like the auto line feed, the software controlled^ character style and although I don't have the lower case modification for the display, the IP-125 will print lower case«

90 U S JOURNAL JULY/AUQ 1079

0 0

Post a comment