C.3.5 Mode 3
Mode 3 provides asynchronous, full-duplex communication, using a total of 11 bits: 1 start
bit, 8 data bits, a programmable 9th bit, and 1 stop bit. The data bits are transmitted and
received LSB first.
The mode 3 transmit and operations are identical to mode 2. The mode 3 baud rate generation
is identical to mode 1. That is, mode 3 is a combination of mode 2 protocol and mode 1 baud
rate. Figure C-15.illustrates the mode 3 transmit timing. Figure C-16.illustrates the mode 3
receive timing.
Mode 3 operation is identical to that of the standard 8051 when Timers 1 and 2 use CLK24/12
(the default).
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-15. Serial Port 0 Mode 3 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-16. Serial Port 0 Mode 3 Receive Timing
C - 26
Appendix C: 8051 Hardware Description
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
