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DS87C550 High-Speed Microcontroller User’s Guide Supplement
47 of 93
REN_1
Bit 4
Receive Enable.
This bit enables/disables the serial port 1 receiver shift register.
0 = Serial port 1 reception disabled.
1 = Serial port 1 receiver enabled (modes 1, 2, 3). Initiate synchronous reception
(mode 0).
TB8_1
Bit 3
9
th
Transmission Bit State.
This bit defines the state of the 9
th
transmission bit
in serial port 1 modes 2 and 3.
RB8_1
Bit 2
9
th
Received Bit State.
This bit identifies the state for the 9
th
reception bit
received data in serial pot 1 modes 2 and 3. In serial port mode 1, when
SM2_1=0, RB8_1 is the state of the stop bit. RB8_1 is not used in mode 0.
TI_1
Bit 1
Transmitter Interrupt Flag.
This bit indicates that data in the serial port 1
buffer has been completely shifted out. In serial port mode 0, TI_1 is set at the
end of the 8
th
data bit. In all other modes, this bit is set at the end of the last data
bit. This bit must be manually cleared by software.
RI_1
Bit 0
Transmitter Interrupt Flag.
This bit indicates that a byte of data has been
received in the serial port 1 buffer. In serial port mode 1, RI_1 is set at the end of
the 8
th
bit. In serial port mode 1, RI_1 is set after the last sample of the incoming
stop bit subject to the state of SM2_1. In modes 2 and 3, RI_1 is set after the last
sample of RB8_1. This bit must be manually cleared by software.
Serial Data Buffer 1 (SBUF1)
7
6
5
4
3
2
1
0
SFR D9h SBUF1.7
SBUF1.6
SBUF1.5
SBUF1.4
SBUF1.3
SBUF1.2
SBUF1.1
SBUF1.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SBUF1.7-0
Bits 7-0
Serial Data Buffer 1.
Data for serial port 1 is read from or written to this
location. The serial transmit and receive buffers are separate registers, but both
are addressed at this location.