參數(shù)資料
型號(hào): ST72121J2
元件分類: 8位微控制器
英文描述: 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash
中文描述: 8位微控制器與2/4/8K字節(jié)在系統(tǒng)可編程閃存
文件頁(yè)數(shù): 66/93頁(yè)
文件大?。?/td> 915K
代理商: ST72121J2
66/93
ST72E121 ST72T121
SERIAL PERIPHERAL INTERFACE
(Cont’d)
5.5.4.2 Slave Configuration
In slave configuration, the serial clock is received
on the SCK pin from the master device.
The value of the SPR0 & SPR1 bits is not used for
the data transfer.
Procedure
– For correct data transfer, the slave device
must be in the same timing mode as the mas-
ter device (CPOL and CPHA bits). See
Figure
38
.
– The SS pin must be connected to a low level
signal during the complete byte transmit se-
quence.
– Clear the MSTR bit and set the SPE bit to as-
sign the pins to alternate function.
In this configuration the MOSI pin is a data input
and the MISO pin is a data output.
Transmit Sequence
The data byte is parallel loaded into the 8-bit shift
register (from the internal bus) during a write cycle
and then shifted out serially to the MISO pin most
significant bit first.
The transmit sequence begins when the slave de-
vice receives the clock signal and the most signifi-
cant bit of the data on its MOSI pin.
When data transfer is complete:
– The SPIF bit is set by hardware
– An interrupt is generated if SPIE bit is set and
I bit in CCR register is cleared.
During the last clock cycle the SPIF bit is set, a
copy of the data byte received in the shift register
is moved to a buffer. When the DR register is read,
the SPI peripheral returns this buffered value.
Clearing the SPIF bit is performed by the following
software sequence:
1. An access to the SR register while the SPIF bit
is set.
2.A read to the DR register.
Notes:
While the SPIF bit is set, all writes to the
DR register are inhibited until the SR 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 5.5.4.6
).
Depending on the CPHA bit, the SS pin has to be
set to write to the DR register between each data
byte transfer to avoid a write collision (see
Section
5.5.4.4
).
66
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