Document # 001-20559 Rev. *D
203
Digital Blocks
17.3.6
SPIM Timing
Enable/Disable Operation.
As soon as the block is config-
ured for SPIM, the primary output is the MSb or LSb of the
shift register, depending on the LSb First configuration in bit
7 of the control register. The auxiliary output is '1' or '0'
depending on the idle clock state of the SPI mode. This is
the idle state.
When the SPIM is enabled, the internal reset is released on
the divide-by-2 flip-flop and on the next positive edge of the
selected input clock. This 1-bit divider transitions to a '1' and
remains free running thereafter.
When the block is disabled, the SCLK and MOSI outputs
revert to their idle state. All internal states are reset (includ-
ing CR0 status) to their configuration-specific reset state,
except for DR0, DR1, and DR2, which are unaffected.
Normal Operation.
Typical timing for an SPIM transfer is
. The user initially
writes a byte to transmit when TX Reg Empty status is true.
If no transmission is currently in progress, the data is loaded
into the shifter and the transmission is initiated. The TX Reg
Empty status is asserted again and the user is allowed to
write the next byte to be transmitted to the TX Buffer regis-
ter. After the last bit is output, if TX Buffer data is available
with one-half clock set up time to the next clock, a new byte
transmission is initiated. An SPIM block receives a byte at
the same time that it sends one. The SPI Complete or RX
Reg Full can be used to determine when the input byte has
been received.
Figure 17-16. Typical SPIM Timing in Mode 0 and 1
INTERNAL CLOCK
TX REG EMPTY
D7
MOSI
D6
D5
D2
D1
D0
D7
User writes first
byte to the TX
Buffer register.
Shifter is loaded
with first byte.
User writes next
byte to the TX
Buffer register.
SCLK (MODE 0)
Shifter is loaded
with next byte.
Last bit of received
data is valid on this
edge and is latched
into RX Buffer.
CLK INPUT
Free running,
internal bit rate
clock is CLK input
divided by two.
Set up time
for TX
Buffer write.
SCLK (MODE 1)
RX REG FULL
First input bit
is latched.
First shift
Содержание PSoC CY8C23533
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