ST7LITE25F2 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
ST7LITE25F2
STMicroelectronics
'ST7LITE25F2' PDF : 170 Pages View PDF
ST7LITE20F2 ST7LITE25F2 ST7LITE29F2
On-chip peripherals
Note:
Note:
Note:
11.4.4
Note:
While the SPIF bit is set, all writes to the SPIDR register are inhibited until the SPICSR
register is read.
Slave mode operation
In slave mode, the serial clock is received on the SCK pin from the master device.
To operate the SPI in slave mode:
1. Write to the SPICSR register to perform the following actions:
– Select the clock polarity and clock phase by configuring the CPOL and CPHA bits
(see Figure 46: Data clock timing diagram).
The slave must have the same CPOL and CPHA settings as the master.
– Manage the SS pin as described in Slave select management and Figure 44:
Generic SS timing diagram. If CPHA=1 SS must be held low continuously. If
CPHA=0 SS must be held low during byte transmission and pulled up between
each byte to let the slave write in the shift register.
2. Write to the SPICR register to clear the MSTR bit and set the SPE bit to enable the SPI
I/O functions.
Slave mode transmit sequence
When software writes to the SPIDR register, the data byte is loaded into the 8-bit shift
register and then shifted out serially to the MISO pin most significant bit first.
The transmit sequence begins when the slave device receives the clock signal and the most
significant bit of the data on its MOSI pin.
When data transfer is complete:
– The SPIF bit is set by hardware.
– An interrupt request is generated if SPIE bit is set and interrupt mask in the CCR
register is cleared.
Clearing the SPIF bit is performed by the following software sequence:
1. An access to the SPICSR register while the SPIF bit is set.
2. A write or a read to the SPIDR register.
While the SPIF bit is set, all writes to the SPIDR register are inhibited until the SPICSR
register is read.
The SPIF bit can be cleared during a second transmission; however, it must be cleared
before the second SPIF bit in order to prevent an Overrun condition (see Section : Overrun
condition (OVR)).
Clock phase and clock polarity
Four possible timing relationships may be chosen by software, using the CPOL and CPHA
bits (See Figure 46: Data clock timing diagram).
The idle state of SCK must correspond to the polarity selected in the SPICSR register (by
pulling up SCK if CPOL=1 or pulling down SCK if CPOL=0).
The combination of the CPOL clock polarity and CPHA (clock phase) bits selects the data
capture clock edge.
Doc ID 8349 Rev 5
95/166
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