MC81F4432
Uart Mode 2 / 3
Tx
Clock
Write to Shift Register (UDAT)
Shift
TxD
D0
D1
D2
D3
D4
D5
D6
D7
TB8
Stop Bit
Start Bit
UTIR
Rx
Clock
RxD
Stop
Bit
D0
D1
D2
D3
D4
D5
D6
D7
RB8
Start Bit
Bit Detect Sample Time
Shift
URIR
Figure 24-4 Timing Diagram for UART Mode 2 and 3 Operation
The mode 2 is exactly same with mode 3 when the BRDAT register value is ‘00h’. In mode 2 the
BRDAT is assumed „00h‟ even whatever value is stored in the BRDAT register. But in mode 3, the
baud rate is changeable by the BRDAT register.
In mode 2 and 3, 11-bits are transmitted (through the TxD (R15) pin) or received (through the RxD
(R14) pin). Each data frame has four components:
-
-
-
-
Start bit ("0")
8 data bits (LSB first)
Programmable 9th data bit
Stop bit ("1")
The 9th data bit to be transmitted can be assigned a value of "0" or "1" by writing the TB8(UCONH.3)
bit. When receiving, the 9th data bit that is received is written to the RB8(UCONH.2) bit, while the stop
bit is ignored.
The baud rate for mode 2 is fu/16 (BRDAT is ignored in mode 2).
The baud rate for mode 3 is fu/(16×(BRDAT+1)).
October 19, 2009 Ver.1.35
155
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