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B y t e / L a n c a s t e r F o r m a t s
To support the Byte/Lancaster Format, the software
tape handler in Appendix B must be used.
The conversion of Biphase Data Formats into Byte/
Lancaster Formats is explained in the following dis
cussion.
Biphase Encoding results in two flux rever
sals per bit (one cycle) when recording a constant
string of ones or zeros; and one flux reversal per
bit (one-half cycle) when recording a string of al
ternating ones, and zeros (see the Theory of Operation
for more d e tail).
ones in the Biphase mode results in eight cycles
being recorded.
and zeros (e.g., 1010 1010 AA Hex) results in four
cylces being recorded.
The Byte/Lancaster standard for recording data
is then achieved by changing the recording speed to
2400 bits/second and recording a byte of FF Hex or
55 Hex to represent a one or zero bit respectively.
For more detailed infromation, the User is referred
to the article by Lancaster in the first issue of
Byte Magazine.
DATA FORMATS
Writing a block of data to cassette consists of
writing a Start Byte (for synchronizing the hardware
data separation logic), a Sync Byte (for software
recognition as a start-of-block indicator), the data
bytes, and a check byte(s).
Reading the data back requires recognizing the
Sync Byte, reading and storing the data bytes and
then using the check bytes to insure the data was
properly transferred.
Appendix B contains subroutines for writing the
Start and Sync Bytes, writing a Data Byte, recog
nizing the Sync Byte and reading a Data Byte.
included
are handlers for writing or reading a block
of 256 bytes using the standard CRC data check for
insuring that the data is proper.
The routines listed in Appendices B and C are re
corded in Tarbell format on the test cassette which
is shipped with the board.
fully described in Appendix A.
Hence, recording a byte of all
Recording a byte of alternating ones
The cassette is mere
MIO
User Guide
Also
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