How Output Data Is Transmitted - Commodore Amiga Hardware Reference Manual

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