In figure 97, wr, At8xc51snd1c – Rainbow Electronics AT89C51SND1C User Manual
Page 136
136
AT8xC51SND1C
4109E–8051–06/03
Figure 97. Transmission Waveforms (Mode 0)
Reception (Mode 0)
To start a reception in mode 0, write to SCON register clearing SM0, SM1 and RI bits
and setting the REN bit.
As shown in Figure 98, Clock is pulsed and the LSB (D0) is sampled on the RXD pin.
The D0 bit is then shifted into the shift register. After eight samplings, the MSB (D7) is
shifted into the shift register, and hardware asserts RI bit to indicate a completed recep-
tion. Software can then read the received Byte from SBUF register.
Figure 98. Reception Waveforms (Mode 0)
Baud Rate Selection (Mode 0)
In mode 0, the baud rate can be either, fixed or variable.
As shown in Figure 99, the selection is done using M0SRC bit in BDRCON register.
Figure 100 gives the baud rate calculation formulas for each baud rate source.
Figure 99. Baud Rate Source Selection (mode 0)
Figure 100. Baud Rate Formulas (Mode 0)
Write to SBUF
TXD
RXD
TI
D0
D1
D2
D3
D4
D5
D6
D7
Write to SCON
TXD
RXD
RI
D0
D1
D2
D3
D4
D5
D6
D7
Set REN, Clear RI
0
1
M0SRC
BDRCON.0
PER
CLOCK
÷
6
To Serial Port
IBRG
CLOCK
Baud_Rate=
6
(1-SPD)
⋅
32
⋅
(256 -BRL)
2
SMOD1
⋅
F
PER
BRL= 256
-
6
(1-SPD)
⋅
32
⋅
Baud_Rate
2
SMOD1
⋅
F
PER
a. Fixed Formula
b. Variable Formula
Baud_Rate
=
6
F
PER