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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Synchronous Serial Port
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
862
Order Number: 306262-004US
20.2.2
Parallel Data Formats for Buffer Storage
Data in buffers is always stored with one sample per 16-bit word regardless of the
format data word length. Within each 16-bit field, stored data sample is right-justified,
with word LSB in bit 0, and unused bits packed as zeroes on left-hand (MSB) side. Logic
in SSP automatically left-justifies data in the Transmit FIFO so that the sample is
properly transmitted on SSP_TXD in the selected frame format.
20.3
Buffer Operation
There are two separate and independent buffers for “incoming” (from peripheral) and
“outgoing” (to peripheral) serial data. Buffers are filled or emptied by an SRAM-like
transfer initiated by the system processor.
Although the system bus is 32 bits wide, only single samples may be transferred. Thus,
only the lower two bytes of the 32 bit word will have valid data; the upper two bytes
are not used and will include dummy or invalid data that should be discarded.
Table 272.
National Microwire
*
Frame Format
SSP
_SC
LK
...
...
SSP
_SF
RM
...
...
SSP
_TX
D
Bit<7>
...
Bit<0>
...
8-Bit Control
1 Clk
SSP
_RX
D
...
Bit<N>
...
Bit<0>
4 to 16 Bits
Single Transfer
SSP
_SC
LK
...
...
...
SSP
_SF
RM
...
...
...
SSP
_TX
D
Bit<0>
...
Bit<7>
...
Bit<0>
...
1 Clk
1 Clk
SSP
_RX
D
Bit<N>
...
Bit<0>
...
Bit<N>
...
Bi
Continuous Transfers