If the above conditions are met, the serial port then writes the received byte to the SBUF0 (or
SBUF1) register, loads the stop bit into RB8_0 (or RB8_1), and sets the RI_0 (or RI_1) bit. If
the above conditions are not met, the received data is lost, the SBUF register and RB8 bit are
not loaded, and the RI bit is not set. After the middle of the stop bit time, the serial port waits
for another high-to-low transition on the RXD0 (or RXD1) pin.
Write to
SBUF0
TX CLK
SHIFT
START
D0
D1
D2
D3
D4
D5
D6
D7
TB8
STOP
TXD0
RXD0
RXD0OUT
TI_0
RI_0
Figure C-13. Serial Port 0 Mode 2 Transmit Timing
RX CLK
RXD0
START
D0
D1
D2
D3
D4
D5
D6
D7
RB8
STOP
Bit detector
sampling
SHIFT
RXD0OUT
TXD0
TI_0
RI_0
Figure C-14. Serial Port 0 Mode 2 Receive Timing
EZ-USB TRM v1.9
Appendix C: 8051 Hardware Description
C - 25
CYPRESS [ CYPRESS ]
