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76 www.xilinx.com SPI-4.2 Lite v4.3 User Guide
UG181 June 27, 2008
Chapter 4: Designing with the Core
R
Reserved Control Words
As defined by the OIF SPI-4.2 specification, a reserved control word contains an SOP, but
the payload control bit (RDat[15]) is not set to a one. If this occurs and is followed by
data, the Sink core asserts SnkFPayloadErr for the duration of the burst, indicating that the
burst did not have a correct payload control word. This indicates that the SOP and address
configuration will not be valid. This error will also be flagged on SnkBusErr. This
behavior is illustrated in Figure 4-20.
If this behavior occurs and is not followed by data, then the Sink core drops the control
word and asserts the output SnkBusErr.
Source Core
Basic Operation
The Source core receives 32-bit or 64-bit data on the user interface and converts data to 16-
bit data which is transferred across the SPI-4.2 interface. It also receives flow control
information of the SPI-4.2 interface and processes it into 32-bit or 2-bit status word,
depending on the status FIFO interface— accessible through the user interface.
The following sections explain how the Source core operates. See “Source Core Interfaces,”
page 30 for the signal list of the interfaces.
Source SPI-4.2 Interface
The SPI-4.2 user interface combines data words and out-of-band control signals and
multiplexes them to the SPI-4.2 16-bit databus. This allows the user interface to run at half
(64-bit interface) or a quarter (32-bit interface) of the data rate. For example, for a 200 Mbps
SPI-4.2 data rate and a 32-bit user interface, you can write data into the Source core at
100 MHz. With a 64-bit user interface, one can write data into the Source core at 50 MHz
and maintain the same data rate.
Figure 4-20: Example of Error Flag SnkFFPayloadErr
IDLE SOP DATA DATA IDLE
Reserved Ctl word detected:
RDat[15]=0
RDat[12]=1
User Interface
DATA
SPI-4.2 Interface
EOP
Addr=prev Addr
SOP=0
Data
SnkFFPayloadErr
Addr
--
Data
SnkFFPayloadErr
Addr
EOP
Data
SnkFFPayloadErr