IBM cassette tape

An IBM PC with just an external cassette recorder for storage can only use the built-in ROM BASIC as its operating system, which supports cassette operations. IBM PC DOS has no native support for cassette tapes, though software can be written to provide support. BIOS interrupt call 15h routines are documented in the technical reference manual that turns the cassette motor on and off, and read or write data. Data is written with a lead-in section, and formatted in 256-byte blocks with a 2-byte CRC. Programmers can also operate the cassette relay by writing to its I/O address. The cassette, disk, advanced, and cartridge versions of IBM BASIC includes statements for cassette operations, but these features only work if the machine had a cassette port. The data transfer speed is from 1-2 kilobits per second, compared to the disk drive's 250 kilobits per second. In 2020, the cassette interfaces of the IBM PC and PCjr were utilized to boot FreeDOS off a custom vinyl disc. ==Data format==

The technical reference for the specifies that the WRITE-BLOCK routine turns on the cassette drive motor and transforms each byte into bits. A (1) bit corresponds to a timer period, (0) bit corresponds to , which results in a recording speed of . First of is written. One synchronization bit . A synchronization byte of . 256-byte blocks of data and a 2-byte CRC is written until all data is transferred. ==Connector pinout==

The IBM PC uses a female 5-pin DIN connector (the same as the keyboard connector) for the cassette port: Pinout: • Pin 1: MOTOR CONTROL COMMON • Pin 2: GND • Pin 3: MOTOR CONTROL (6 V/1 A) RELAY • Pin 4: DATA-IN (500 nA with 13 V at 1000-2000 Baud) • Pin 5: DATA-OUT (250 μA jumperable either at 0.68 V ("AUX") or 75 mV ("MIC")) Motor control: 8255A port , bit : = on, = off. ==See also==