Serial Peripheral Interface Controller
UG0331 User Guide Revision 15.0
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14.2.2.4 National Semiconductor MICROWIRE Protocol
The National Semiconductor MICROWIRE serial interface is a half-duplex protocol using a master/slave
message passing technique. Each serial transmission begins with an 8-bit control word, during which
time no incoming data is received. After the control word is sent, the external slave decodes it, and after
waiting one serial clock cycle from the end of the control word, responds with the required data, which
may be 4 to 16 bits in length.
14.2.2.4.1 Single Frame Transfer
In single frame transfer mode (shown in the following figure), the most significant byte of the FIFO
transmit word is the control byte. The total data frame size supplied must be at least 12 bits long (8 bits
for the control word and a minimum of 4 bits for data payload). Only the output data is sampled and
inserted in the receive FIFO.
Figure 214 •
National Semiconductor MICROWAVE Single Frame Transfer
14.2.2.4.2 Multiple Frame Transfer
In the multiple frame transfer (shown in the following figure), the slave select signal (SPI_X_SS[x]) is
continuously asserted (held Low) while SPI_X_DOE_N (output Enable) is also asserted (or held Low) for
the duration of each control byte. The other data transfers proceed in back-to-back manner.
Figure 215 •
National Semiconductor MICROWIRE Multiple Frame Transfer
4 to 16 Bits
Output Data
SPI_CLK
SPI_DI
SPI_DOE_N
SPI_DO
SPI_SS[x]
8-Bit Control
MSB
LSB
LSB
MSB
0
8-Bit Control
4 to 16 Bits
Output Data
SPI_CLK
SPI_DI
SPI_DOE_N
SPI_DO
SPI_SS[x]
MSB
MSB
LSB
LSB
LSB
MSB
0