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13.1.4 Special Mode 2 (UART2)
Multiple slaves can be serially communicated from one master. Transfer clock polarity and phase are
selectable. Table 13.1.4.1 lists the specifications of Special Mode 2. Table 13.1.4.2 lists the registers
used in Special Mode 2 and the register values set. Figure 13.1.4.1 shows communication control ex-
ample for Special Mode 2.
Table 13.1.4.1. Special Mode 2 Specifications
Item
Transfer data format
Transfer clock
Transmit/receive control
Transmission start condition
Reception start condition
Interrupt request
generation timing
Error detection
Select function
NOTES:
1. When an external clock is selected, the conditions must be met while if the CKPOL bit in the U2C0 register "0"
(transmit data output at the falling edge and the receive data taken in at the rising edge of the transfer clock), the
external clock is in the high state; if the CKPOL bit in the U2C0 register "1" (transmit data output at the rising edge
and the receive data taken in at the falling edge of the transfer clock), the external clock is in the low state.
2. If an overrun error occurs, bits 8 to 0 in UiRB register are undefined. The IR bit in the SiRIC register remains
unchanged.
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• Transfer data length: 8 bits
• Master mode
The CKDIR bit in the U2MR register is set to "0" (internal clock) : fj/ (2(n+1))
fj = f
, f
, f
1SIO
2SIO
• Slave mode
The CKDIR bit is set to "1" (external clock selected) : Input from CLK2 pin
Controlled by input/output ports
• Before transmission can start, the following requirements must be met
_
The TE bit in the U2C1 register is set to "1" (transmission enabled)
_
The TI bit in the U2C1 register is set to "0" (data present in U2TB register)
• Before reception can start, the following requirements must be met
_
The RE bit in the U2C1 register is set to "1" (reception enabled)
_
The TE bit in the U2C1 register is set to "1" (transmission enabled)
_
The TI bit in the U2C1 register is set to "0" (data present in the U2TB register)
• While transmitting, one of the following conditions can be selected
_
The U2IRS bit in the U2C1 register is set to "0" (transmit buffer empty): when trans-
ferring data from the U2TB register to the UART2 transmit register (at start of transmission)
_
The U2IRS bit is set to "1" (transfer completed): when the serial I/O finished sending
data from the UART2 transmit register
• While receiving
When transferring data from the UART2 receive register to the U2RB register (at
completion of reception)
(2)
• Overrun error
This error occurs if the serial I/O started receiving the next data before reading the
U2RB register and received the 7th bit of the next data
• Clock phase setting
Selectable from four combinations of transfer clock polarities and phases
page 168
f o
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Specification
, f
. n: Setting value of U2BRG register
8SIO
32SIO
13. Serial I/O
00
to FF
16
16
(1)
(1)
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