Motorola DSP56301 - Manual (Page 232)

ESSI Programming Model
7 -34 DSP56301 User’s Manual
TSMA and TSMB (as in Figure 7-12 and Figure 7-13) can be seen as a single 32-bit register,
TSM. Bit n in TSM (TSn) is an enable/disable control bit for transmission in slot number N.
When TSn is cleared, all the data signals of the enabled transmitters are tri-stated during
transmit time slot number N. The data still transfers from the enabled transmit data register(s)
to the transmit shift register. However, the TDE and the TUE flags are not set. Consequently,
during a disabled slot, no transmitter empty interrupt is generated. The DSP is interrupted
only for enabled slots. Data written to the transmit data register when the transmitter empty
interrupt request is serviced transmits in the next enabled transmit time slot. When TSn is set,
the transmit sequence proceeds normally. Data transfers from the TX register to the shift
register during slot number N, and the TDE flag is set. The TSM slot mask does not conflict
with the TSR. Even if a slot is enabled in the TSM, you can chose to write to the TSR to
tri-state the signals of the enabled transmitters during the next transmission slot. Setting the
bits in the TSM affects the next frame transmission. The frame being transmitted is not
affected by the new TSM setting. If the TSM is read, it shows the current setting.
After a hardware RESET signal or software RESET instruction, the TSM register is reset to
$FFFFFFFF, enabling all 32 slots for data transmission.
23 22 21 20 19 18 17 16 15 14 13 12
TS31 TS30 TS29 TS28
11 10 9 8 7 6 5 4 3 2 1 0
TS27 TS26 TS25 TS24 TS23 TS22 TS21 TS20 TS19 TS18 TS17 TS16
—Reserved bit; read as 0; write to 0 0 for future compatibility.
(ESSI0 X:$FFFFB3, ESSI1 X:$FFFFA3)
Figure 7-15. ESSI Transmit Slot Mask Register B (TSMB)