Motorola DSP56301 - Manual (Page 226)

ESSI Programming Model
7 -28 DSP56301 User’s Manual
7.5.3 ESSI Status Register (SSISR)
The SSISR is a read-only status register by which the DSP reads the ESSI status and serial
input flags.
Figure 7-11. ESSI Status Register (SSISR)
23 22 21 20 19 18 17 16 15 14 13 12
11 10 9 8 7 6 5 4 3 2 1 0
RDF TDE ROE TUE RFS TFS IF1 IF0
—Reserved bit; read as 0; write to 0 0 for future compatibility.
(ESSI0 X:$FFFFB7, ESSI1 X:$FFFFA7)
Table 7-5. ESSI Status Register (SSISR) Bit Definitions
Bit Number Bit Name Reset Value Description
23–8 0 Reserved. Write to 0 for future compatibility.
7 RDF 0 Receive Data Register Full
Set when the contents of the receive shift register transfer to the receive
data register. RDF is cleared when the DSP reads the receive data
register. If RIE is set, a DSP receive data interrupt request is issued when
RDF is set.
6 TDE 0 Transmit Data Register Empty
Set when the contents of the transmit data register of every enabled
transmitter are transferred to the transmit shift register. It is also set for a
TSR disabled time slot period in Network mode (as if data were being
transmitted after the TSR has been written). When TDE is set, TDE data is
written to all the TX registers of the enabled transmitters or to the TSR.
The TDE bit is cleared when the DSP writes to all the transmit data
registers of the enabled transmitters, or when the DSP writes to the TSR
to disable transmission of the next time slot. If the TIE bit is set, a DSP
transmit data interrupt request is issued when TDE is set.
5 ROE 0 Receiver Overrun Error Flag
Set when the serial receive shift register is filled and ready to transfer to
the receive data register (RX) but RX is already full (that is, the RDF bit is
set). If the REIE bit is set, a DSP receiver overrun error interrupt request is
issued when the ROE bit is set. The programmer clears ROE by reading
the SSISR with the ROE bit set and then reading the RX.
4 TUE 0 Transmitter Underrun Error Flag
Set when at least one of the enabled serial transmit shift registers is empty
(that is, there is 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 registers not written) is retransmitted. In Normal
mode, there is only one transmit time slot per frame. In Network mode,
there can be up to 32 transmit time slots per frame. If the TEIE bit is set, a
DSP transmit underrun error interrupt request is issued when the TUE bit
is set. The programmer can also clear TUE by first reading the SSISR with
the TUE bit set, then writing to all the enabled transmit data registers or to
the TSR.