Using my new Timex 2068 for about a week before the April Sincus meeting I was very impressed with the new basic commands which were not available on the T/S 1000 and the keyboard was a great improvement for my “fumbling fingers”, however I was itching to get my printer attached to the expansion slot. I was disappionted with the lack of technical information provided by the user manual as I contemplated how I could get “under the hood” without having my investment turn into a puff of smoke. Thanks to Wes with the technical information he provided at the meeting the next day I had my Epson RX-80 printing data from the 2068.
The 2068 uses ascii character codes for the character set which eliminated a decode table as was necessary with the T/S1000 so it was only a matter of the hardware connection which can be accomplished with four inexpensive integrated circuits. I chose to use a 74LS138,74LS32,74LS373 and a 74LS03 because I had all of them in my junk box. These circuits were sufficient to provide the necessary address decode and data bus isolation for the printer Centronics Interface. Power is provided by the 5 volt pin on the expansion connector. The port address is hex 87 as defined by the Timex Technical Memo #6 to be a Rd/Wr Centronics Interface. Write data is buffered by the 74LS373 and the read is gated by the 74LS03 open collector.
Driving the interface requires a machine code routine of 16 bytes and basic routines to format the data for line and column control. The basic commands COPY, L PRINT and L LIST will not work so all the printing will require a basic routine with a USR call to the machine code. This inconvenience is offset by the ability to print up to 80 columns with selectable type at speeds up to 100 characters per second. With the use of basic routines to provide the data all of the available features of the Epson printer can be used including the dot addressable graphics.
Using basic to format the data for the printer does slow the printer down to some extent. The printing time for this article using basic is about two minutes, the same data when printed using a machine code routine is less than 50 seconds. The equilavent basic routine for the COPY command requires the use of the SCREEN command and some for-next loops,because the display file contains pixel data unlike the T/S 1000 which contained the character code. As more information becomes available about the 2068, converting frequently used print routines to machine code will improve the printing speed and reduce the amount of basic programming.
For the last two weeks since I received my 2068 I have spent many entertaining hours learning the new basic commands and experimenting with some new hardware projects. My next project will be a modem to connect to the outside world. So far the 2068 appears to be a good machine for hardware “add on’s”. I’m hoping to hear from other users about their ideas and interests in hardware.