Table of Contents
7. USART Operation
USART operates in operation mode 0 for normal bidirectional serial communication, in mode 2
and 3 in bidirectional communication as master or slave, and in mode 1 as master or slave in
multiprocessor communication.
■ Operation of USART
• Operation modes
There are four USART operation modes: modes 0 to 3. As listed in table 7-1, an operation mode can be
selected according to the inter-CPU connection method and data transfer mode.
Table 7-1 USART operation mode
Operation
mode
0
normal mode
1
multiprocessor
2
normal mode
3
LIN mode
* means the data bit transfer format: LSB or MSB first
** "+1" means the indicator bit of the address/data selection in the multiprocessor mode, instead of parity.
(Note)
Mode 1 operation is supported both for master or slave operation of USART in a master-slave
connection system. In Mode 3 the USART function is locked to 8N1-Format, LSB first.
If the mode is changed, USART cuts off all possible transmission or reception and awaits then new action.
■ Inter-CPU Connection Method
External Clock One-to-one connection (normal mode) and master-slave connection (multiprocessor mode) can
be selected. For either connection method, the data length, whether to enable parity, and the synchronization
method must be common to all CPUs. Select an operation mode as follows:
• In the one-to-one connection method, operation mode 0 or 2 must be used in the two CPUs. Select
operation mode 0 for asynchronous transfer mode and operation mode 2 for synchronous transfer mode.
Note, that one CPU has to set to the master and one to the slave in synchronous mode 2.
• Select operation mode 1 for the master-slave connection method and use it either for the master or slave
system.
■ Synchronization Methods
In asynchronous operation USART reception clock is automatically synchronized to the falling edge of a
received start bit.
In synchronous mode the synchronization is performed either by the clock signal of the master device or by
USART itself if operating as master.
■ Signal Mode
USART can treat data in non-return to zero (NRZ) and return to zero (RZ) format. For this option the ECCR:
INV bit is provided.
■ Operation Enable Bit
USART controls both transmission and reception using the operation enable bit for transmission (SCR04:
Data length
parity
parity
disabled
enabled
7 or 8
7 or 8 + 1**
-
8
8
-
Chapter 32 USART (LIN / FIFO)
Synchroniza-
Length
tion of mode
of
stop bit
asynchronous
1 or 2
asynchronous
1 or 2
synchronous
0, 1 or 2
asynchronous
1
7.USART Operation
data bit
directio
n*
L/M
L/M
L/M
L
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