The primary feature added by version 1.92 is support of the 88-C700 Centronics printer interface. This emulation piggy-backs onto the 2nd serial port in the Altair Clone just like the 88-LPC printer interface that is already present. However, there is one restriction: The serial port device (88-2SIO or 88-SIO) and the Centronics printer device cannot both use interrupts at the same time. This means, for example, when running Timesharing BASIC, you can't use serial port 2 as both a 2SIO user terminal port and the Centronics printer port at the same time. Under normal BASIC however, you could use both ports at the same time since they are not interrupt driven.
Here is the revision history for the update:
- Add support for the 88-C700 Centronics printer interface. This emulation piggy-backs onto the 2nd serial port in the Altair Clone just like the 88-LPC printer interface that is already present. The Centronics printer interface is selected in BASIC with a "C" response at the printer type prompt. The Centronics interface supports interrupts and is required to use the Altair Accounting package and Time Sharing BASIC as the 88-LPC (Okidata) printer type is not supported by these software packages.
- Update the configuration monitor to allow selection of the printer type (88-LPC Okidata, 88-C700 Centronics, or neither).
- An INPUT from either printer data register now returns 0FFh as with the real hardware (the boards do not respond, so the CPU sees 0FFh on the data input bus). Previously, a value other than 0FFh was returned so programs could detect the presence of the port, but since this is not how the real hardware worked, this has been updated.
- When single stepping from the front panel, previous firmware versions sent OUT data for the 88-LPC through serial port 1 on the Clone instead of serial port 2. This has been fixed.