Bit
Number
Name
15
OVRUN
14 RBF
13
TBE
12
TSRE
242
Interface Hardware
Table 8-10: SERDATR Register
Function
OVERRUN
bit
(Mirror-also
appears
in
the interrupt request
register.) Indicates
that
another byte of
data
was received before the previous byte was picked
up
by
the processor.
To
prevent this condition,
it
is
necessary
to
reset the RBF bit (bit
11)
(receive-buffer-full) in the interrupt request
register (INTREQ).
READ BUFFER FULL
(Mirror-also
appears
in
the interrupt request
register.) When it
is
a
1,
it
says
that
there is
data
ready
to
be picked up by the processor.
After reading the contents of this
data
register,
you must reset the RBF bit in INTREQ
to
prevent
an overrun.
TRANSMIT BUFFER
EMPTY
(Not a
mirror-interrupt
occurs when the
buffer
becomes empty.) When
it
is a
1,
the
data
in the
output
data
register (SERDAT)
has been transferred
to
the serial
output
shift
register, so SERDAT
is
ready
to
accept another
output
word. This is also true when the buffer
is empty.
This bit
is
normally used for full-duplex operation.
TRANSMIT SHIFT REGISTER
EMPTY
When this bit
is
a
1,
the
output
shift register
has completed its task, all
data
has been
transmitted, and the register is now idle.
If you stop writing
data
into the
output
register (SERDAT), then this bit will
become a 1 after both the word currently
in the shift register
and the word
placed into SERDAT have been transmitted.
This bit is normally used for half-duplex operation.
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