IBM 5150 Technical Reference

sync byte (ASCII character hex 16) is read. If the sync byte is
read correctly, the data portion can be read. If a correct sync
byte
is not found, the routine goes back and searches for the
leader again. The data
is read a bit at a time and assembled into
bytes. After each byte
is assembled, it is written into memory at
location ES:BX and
BX is incremented by 1.
After each multiple of 256 data bytes is read, the CRC is read
and compared to the
CRC generated. If a CRC error is detected,
the routine exits with the carry flag set to indicate an error and
the status of
AH set to hex 01. DX contains the number of bytes
written to memory.
The time of day interrupt(IRQO)
is disabled during the
cassette-read operation.
Data Record Architecture
The write-block routine uses the following format to record a tape
block onto a cassette tape.
Component
Description
Leader 256 Bytes (of All 1 's)
Sync Bit
One 0 Bit
Sync
Byte
ASCII Character Hex 16
Data Blocks
256 Bytes in Length
CRC
2 Bytes for each Data Block
Data Record Components
System BIOS 5-27

IBM 5150 Specifications

General

Brand	IBM
Model	5150
Category	Desktop
Language	English