11
RXD
Direct read of
RXD
pin on Paula chip.
10
Not used
at
this time
9
STP
Stop bit if 9
data
bits are specified for
receive.
8
STP
Stop bit if 8
data
bits are specified for
receive,
OR
DB8
9th
data
bit if 9 bits are specified for
receIve.
7-0
DB7-DBO
Low
8
data
bits of received data.
Data
is TRUE (data you read·
is
the same
polarity as the
data
expected).
HOW
OUTPUT
DATA
IS
TRANSMITTED
You send
data
out on the transmit lines by writing into the serial
data
output
register
(SERDAT). This register
is
write-only.
Data
will
be
sent
out
at
the same rate as you have established for the read, and this
data
is
contained
in
the serial
data
period register (SERPER) shown above. Immediately
after you write the
data
into this register, the system will begin the transmission
at
the
baud rate you selected.
At the
start
of the operation, this
data
is
transferred from SERDAT into a serial shift
register. When the transfer to the serial shift register has been completed, SERDAT can
accept new data; the TBE interrupt signals this fact.
Data
will be moved
out
of the shift register, one bit during each time interval, starting
with the least significant bit. The shifting continues until, following the last shift, the
UART detects the condition "shift-register-empty," which means
that
only
Os
remain
in
the register.
SERDAT
is
a 16-bit register
that
allows you to control the format (appearance) of the
transmitted data.
To
form a typical
data
sequence, such as one
start
bit, eight
data
bits, and two stop bits, you write into SERDAT the contents shown
in
figures 8-4 and
8-5.
Interface Hardware
243
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