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Existing Device Drivers

VTCOM.DEV is the device driver for the VTCOM Tape Drive Simulation Software running at MS-DOS PC connected via Serial Port (RS-232) to LC-81. This program simulates a Tape Drive according to the "LC-81 Tape Drives Specification". (See the specification in section "Specs").

The LC-81 serial port is based on UART chip 16C550. The INIT routine initializes the chip to use FIFO and to interrupt for each byte received.

Since there is no EXT-BUS in this case, Drive's registers C and F can not be accessed directly. Access to those registers is orchestrated by the mean of 3-bytes "Escape Sequences". This method, however, presents a limitation for interrupts associated to the WRITE operation: it is not practical to write one byte at the time (as specified for Tape Drives) so the ISR routine writes a whole block continuously in a loop before returning.

We will cover VTCOM Operations and Escape Sequences in details later in section "VTCOM Tape Drive Simulation Software".