Motorola* Spi Frame Format; Microwire* Format — Details - Intel IXP45X Developer's Manual

Synchronous Serial Port—Intel
Table 271. Motorola
SSP_
SCLK
SSP_S
FRM
SSP_T
XD
SSP_R
XD
SSP_S
CLK
SSP_S
FRM
TX/RX
Note: The phase and polarity of SSP_SCLK can be configured for four different modes. This example shows
just one of those modes.
20.2.1.3 Microwire* Format — Details
This format is similar to SPI, except transmission is half-duplex instead of full-duplex,
using master-slave message passing.
In idle state or when the SSP is disabled, SSP_SCLK is low, SSP_SFRM is high and
SSP_TXD is low. Each serial transmission begins with SSP_SFRM assertion (low),
followed by an 8-bit or 16-bit command word sent from controller to peripheral on
SSP_TXD. SSP_RXD, controlled by the peripheral, remains tri-stated. SSP_SCLK
goes high midway into the command MSB and continues toggling at the bit rate. One
bit-period after the last command bit, the peripheral returns the serial data requested,
MSB first, on SSP_RXD. Data transitions on falling edge of SSP_SCLK and is sampled
on the rising edge. The last falling edge of SSP_SCLK coincides with the end of the last
data bit (LSB) on SSP_RXD, and it remains low after that (if the only, or last word, of
the transfer). SSP_SFRM deasserts high one-half clock period later.
The start and end of a series of back-to-back transfers are like those of a single
transfer; however, SSP_SFRM remains asserted (low) throughout the transfer. The
end of a data word on SSP_RXD is followed immediately by the start of the next
command byte on SSP_TXD, with no "dead" time.
Table 272
and when back-to-back frames are transmitted.
August 2006
Order Number: 306262-004US
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
*
SPI Frame Format
Bit<N>
Bit<N>
MSB
Bit<N..
Bit<0> Bit<N>
1>
shows the National Microwire frame format for a single transmitted frame
...
...
Bit<N..
... Bit<1> Bit<0>
1>
Bit<N..
... Bit<1> Bit<0>
1>
4 to 16 Bits LSB
Single Transfer
...
...
... Bit<1> Bit<0> Bit<N>
Continuous Transfers
® ®
Intel IXP45X and Intel IXP46X Product Line of Network Processors
...
...
Bit<N..
... Bit<1> Bit<0>
1>
Developer's Manual
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