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Document # 001-20559 Rev. *D
Digital Blocks
17.1.11.1
Usability Exceptions
The following are usability exceptions for the SPI protocol
function.
1. The SPIM function may not be chained.
2. The MISO input must be resynchronized at the row
inputs.
3. The DR2 (Rx Buffer) register is not writeable.
17.1.11.2
Block Interrupt
The SPIM block has a selection of two interrupt sources:
Interrupt on TX Reg Empty (default) or interrupt on SPI
Complete. Mode bit 1 in the function register controls the
selection. These modes are discussed in detail in
.
If SPI Complete is selected as the block interrupt, the control
register must be read in the interrupt routine so that this sta-
tus bit is cleared; otherwise, no subsequent interrupts are
generated.
17.1.12
SPI Slave Function
The SPI Slave (SPIS) offers SPI operating modes 0-3. By
default, the MSb of the data byte is shifted out first. An addi-
tional option can be set to reverse the direction and shift the
data byte out LSb first. (Refer to the timing diagrams for this
function on page
.)
When configured for SPI, DR0 functions as a shift register,
with input from the DATA input (MOSI) and output to the pri-
mary output F1 (MISO). DR1 is the TX Buffer register and
DR2 is the RX Buffer register.
The SPI protocol requires data to be registered at the device
input, on the opposite edge of the clock that operates the
output shifter. An additional register (RXD), at the input to
the DR0 shift register, is implemented for this purpose. This
register stores received data for one-half cycle before it is
clocked into the shift register.
The SPIS function derives all clocking from the SCLK input
(typically an external SPI master). This means that the mas-
ter must initiate all transmissions. For example, to read a
byte from the SPIS, the master must send a byte.
There are 4 control bits and 4 status bits in the control regis-
ter that provide for PSoC device interfacing and synchroni-
zation.
In the SPIS, there is an additional data input, Slave Select
(SS_), which is an
signal. SS_ must be asserted
to enable the SPIS to receive and transmit. SS_ has two
high level functions: 1) To allow for the selection of a given
slave in a multi-slave environment, and 2) To provide addi-
tional clocking for TX data queuing in SPI modes 0 and 1.
SS_ may be controlled from an external pin through a Row
Input or by way of user firmware.
When SS_ is negated, the SPIS ignores any MOSI/SCLK
input from the master. In addition, the SPIS
is reset, and the MISO output is forced to idle at logic 1. This
allows for a wired-AND connection in a multi-slave environ-
ment. Note that if High Z output is required when the slave is
not selected, this behavior must be implemented in firmware
with IO writes to the port drive register.
17.1.12.1
Usability Exceptions
A usability exception for the SPI slave function.
1. The SPIS function may not be chained.
17.1.12.2
Block Interrupt
The SPIS block has a selection of two interrupt sources:
Interrupt on TX Reg Empty (default) or interrupt on SPI
Complete (same selection as the SPIM). Mode bit 1 in the
function register controls the selection.
If SPI Complete is selected as the block interrupt, the control
register must still be read in the interrupt routine so that this
status bit is cleared; otherwise, no subsequent interrupts are
generated.
Содержание PSoC CY8C23533
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