SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 92
PORT C
MOTOROLA
6.4.2.2.11
CRB SSI Mode Select (MOD) Bit 11
MOD selects the operational mode of the SSI. When MOD is cleared, the normal mode is
selected; when MOD is set, the network mode is selected. In the normal mode, the frame
rate divider determines the word transfer rate – one word is transferred per frame sync
during the frame sync time slot. In network mode, a word is (possibly) transferred every
time slot. For more details, see 6.4.3. Hardware and software reset clear MOD.
6.4.2.2.12
CRB SSI Transmit Enable (TE) Bit 12
TE enables the transfer of data from TX to the transmit shift register. When TE is set and
a frame sync is detected, the transmit portion of the SSI is enabled for that frame. When
TE is cleared, the transmitter will be disabled after completing transmission of data cur-
rently in the SSI transmit shift register. The serial output is three-stated, and any data
present in TX will not be transmitted (i.e., data can be written to TX with TE cleared; TDE
will be cleared, but data will not be transferred to the transmit shift register).
The normal mode transmit enable sequence is to write data to TX or TSR before setting
TE. The normal transmit disable sequence is to clear TE and TIE after TDE equals one.
In the network mode, the operation of clearing TE and setting it again will disable the
transmitter after completing transmission of the current data word until the beginning of
the next frame. During that time period, the STD pin will remain in the high-impedance
state. Hardware reset and software reset clear TE.
The on-demand mode transmit enable sequence can be the same as the normal mode,
or TE can be left enabled.
Note: TE does not inhibit TDE or transmitter interrupts. TE does not affect the generation
of frame sync or output flags.
6.4.2.2.13
CRB SSI Receive Enable (RE) Bit 13
When RE is set, the receive portion of the SSI is enabled. When this bit is cleared, the
receiver will be disabled by inhibiting data transfer into RX. If data is being received while
this bit is cleared, the remainder of the word will be shifted in and transferred to the SSI
receive data register.
RE must be set in the normal mode and on-demand mode to receive data. In network
mode, the operation of clearing RE and setting it again will disable the receiver after re-
ception of the current data word until the beginning of the next data frame. Hardware and
software reset clear RE.
Note: RE does not inhibit RDF or receiver interrupts. RE does not affect the generation
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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