
MC68HC08AS20
—
Rev. 4.1
Advance Information
Freescale Semiconductor
333
Logic 1
A logic 1 is defined as either:
–
An active-to-passive transition followed by a passive period
128
μ
s in length, or
–
A passive-to-active transition followed by an active period
64
μ
s in length
See
Figure 20-6
(b)
.
Normalization Bit (NB)
The NB symbol has the same property as a logic 1 or a logic 0. It is
only used in IFR message responses.
Break Signal (BREAK)
The BREAK signal is defined as a passive-to-active transition
followed by an active period of at least 240
μ
s (see
Figure 20-6
(c)
).
Start-of-Frame Symbol (SOF)
The SOF symbol is defined as passive-to-active transition followed by
an active period 200
μ
s in length (see
Figure 20-6
(d)
). This allows the
data bytes which follow the SOF symbol to begin with a passive bit,
regardless of whether it is a logic 1 or a logic 0.
End-of-Data Symbol (EOD)
The EOD symbol is defined as an active-to-passive transition
followed by a passive period 200
μ
s in length (see
Figure 20-6
(e)
).
End-of-Frame Symbol (EOF)
The EOF symbol is defined as an active-to-passive transition followed
by a passive period 280
μ
s in length (see
Figure 20-6
(f)
). If no IFR
byte is transmitted after an EOD symbol is transmitted, after another
80
μ
s the EOD becomes an EOF, indicating completion of the
message.
Inter-Frame Separation Symbol (IFS)
The IFS symbol is defined as a passive period 300
μ
s in length. The
20-
μ
s IFS symbol contains no transition, since when it is used it
always appends to a 280-
μ
s EOF symbol (see
Figure 20-6
(g)
).