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R8C/14 Group, R8C/15 Group 15. Clock Synchronous Serial I/O with Chip Select (SSU)
Rev.2.10 Jan 19, 2006 Page 155 of 253
REJ09B0164-0210
15.5.2 Data Transmit
Figure 15.12 shows an Example of SSU Operation for Data Transmit (Clock Synchronous
Communication Mode). During the data transmit, the SSU operates as described below.
When the SSU is set as a master device, it outputs a synchronous clock and data.
When the SSU is set as a slave device, it outputs data synchronized with the input clock. When
setting the TE bit to “1” (enables transmit) before writing the transmit data to the SSTDR register, the
TDRE bit is automatically set to “0” (data is not transferred from the SSTDR to SSTRSR registers)
and the data is transferred from the SSTDR to SSTRSR registers.
After the TDRE bit is set to “1” (data is transferred from the SSTDR to SSTRSR registers), a transmit
is started. When the TIE bit in the SSER register is set to “1”, the TXI interrupt request is generated.
When one frame of data is transferred while the TDRE bit is set to “0”, data is transferred from the
SSTDR to SSTRSR registers and a transmit of the next frame is started. If the 8th bit is transmitted
while the TDRE bit is set to “1”, the TEND bit in the SSSR register is set to “1” (the TDRE bit is set to
“1” when the last bit of the transmit data is transmitted) and the state is retained. The TEI interrupt
request is generated when the TEIE bit in the SSER register is set to “1” (enables transmit-end
interrupt request). The SSCK pin is retained “H” after transmit-end.
Transmit can not be performed while the ORER bit in the SSRR register is set to “1” (overrun error
occurs). Confirm that the ORER bit is set to “0” before transmit.
When setting the microcomputer to the slave device, ensure the TEND bit is set to “1” (data transmit
ends) and write the following transmit data to the SSTDR register. When setting the microcomputer to
the master device, continuous transmit is enabled.
Figure 15.13 shows a Sample Flowchart for Data Transmit (Clock Synchronous Communication
Mode).
Figure 15.12 Example of SSU Operation for Data Transmit (Clock Synchronous Communication
Mode)
SSCK
b0
SSO
When SSUMS=0 (clock synchronous communication mode), CPHS=0 (data change
at odd numbers) and CPOS=0 (“H” when clock stops)
b1 b7b0 b1b7
1 Frame
TDRE Bit in
SSSR Register
“0”
“1”
TEND Bit in
SSSR Register
“0”
“1”
TEI interrupt request
generation
Write data to SSTDR register
Process by
Program
1 Frame
TXI interrupt request generation
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