Figure 76. National Semiconductor Microwire Frame Format, Continuous Transfers - Wiznet W7500 Reference Manual

transferred to the serial shift register of the transmit logic and the MSB of the 8-bit control
frame to be shifted out onto the SSPTXD pin. SSPFSSOUT remains LOW for the duration of
the frame transmission. The SSPRXD pin remains tristated during this transmission.
The off-chip serial slave device latches each control bit into its serial shifter on the rising
edge of each SSPCLKOUT. After the last bit is latched by the slave device, the control byte is
decoded during a one clock wait-state and the slave responds by transmitting data back to
the PrimeCell SSP. Each bit is driven onto the SSPRXD line on the falling edge of SSPCLKOUT.
The PrimeCell SSP in turn latches each bit on the rising edge of SSPCLKOUT. At the end of the
frame for single transfers, the SSPFSSOUT signal is pulled HIGH one clock period after the
last bit has been latched in the receive serial shifter, which causes the data to be
transferred to the receive FIFO.
The off-chip slave device can tristate the receive line either on the falling edge of
SSPCLKOUT after the LSB has been latched by the receive shifter or when the SSPFSSOUT pin
goes HIGH.
For continuous transfers, data transmission begins and ends in the same manner as a single
transfer. However, the SSPFSSOUT line is continuously asserted, held LOW, and transmission
of data occurs back-to-back. The control byte of the next frame follows directly after the
LSB of the received data from the current frame. Each of the received values is transferred
from the receive shifter on the falling edge SSPCLKOUT, after the LSB of the frame has been
latched into the PrimeCell SSP.
Figure 76 shows the National Semiconductor Microwire frame format when back-to-back
frames are transmitted.
SSPCLKOUT/
SSPCLKIN
SSPFSSOUT/
SSPFSSIN
SSPTXD
SSPRXD
nSSPOE
Figure 76.
National Semiconductor Microwire frame format, continuous transfers
W7500 Datasheet Version1.0.0
LSB
LSB
4 to 16 bits
output data
MS
0
MSB
B
MSB LSB
8-bit control
LSB LSB
LSB MSB
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