SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 96
PORT C
MOTOROLA
MOVEP
X:SSIRx,X:(R4)+
JCLR
#3,X:SSISR,_NoRFS ;1 = FIRST TIMESLOT
;Do something
JMP
_DONE
_NoRFS
;Do something else
_DONE
Note: In normal mode, RFS will always read as a one when reading data because there
is only one time slot per frame – the “frame sync” time slot.
RFS, which is cleared by hardware, software, SSI individual, or STOP reset, is not affect-
ed by RE.
6.4.2.3.5
SSISR Transmitter Underrun Error Flag (TUE) Bit 4
TUE is set when the serial transmit shift register is empty (no new data to be transmitted)
and a transmit time slot occurs. When a transmit underrun error occurs, the previous data
(which is still present in the TX) will be retransmitted.
In the normal mode, there is only one transmit time slot per frame. In the network mode,
there can be up to 32 transmit time slots per frame.
TUE does not cause any interrupts; however, TUE does cause a change in the interrupt
vector used for transmit interrupts so that a different interrupt handler may be used for a
transmit underrun condition. If a transmit interrupt occurs with TUE set, the transmit data
with exception status interrupt will be generated; if a transmit interrupt occurs with TUE
clear, the transmit data without errors interrupt will be generated.
Hardware, software, SSI individual, and STOP reset clear TUE. TUE is also cleared by
reading the SSISR with TUE set, followed by writing TX or TSR.
6.4.2.3.6
SSISR Receiver Overrun Error Flag (ROE) Bit 5
This flag is set when the serial receive shift register is filled and ready to transfer to the
receiver data register (RX) and RX is already full (i.e., RDF=1). The receiver shift register
is not transferred to RX. ROE does not cause any interrupts; however, ROE does cause
a change in the interrupt vector used for receive interrupts so that a different interrupt han-
dler may be used for a receive error condition. If a receive interrupt occurs with ROE set,
the receive data with exception status interrupt will be generated; if a receive interrupt oc-
curs with ROE clear, the receive data without errors interrupt will be generated.
Hardware, software, SSI individual, and STOP reset clear ROE. ROE is also cleared by read-
ing the SSISR with ROE set, followed by reading the RX. Clearing RE does not affect ROE.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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