Motorola DSP56301 - Manual (Page 233)

ESSI Programming Model
Enhanced Synchronous Serial Interface (ESSI) 7 -35
7.5.10 Receive Slot Mask Registers (RSMA, RSMB)
Both receive slot mask registers are read/write registers. In Network mode, the receiver(s) use
these registers to determine which action to take in the current time slot. Depending on the
setting of the bits, the receiver(s) either tri-state the receiver(s) data signal(s) or receive a data
word and generate a receiver full condition.
RSMA and RSMB (as in Figure 7-12 and Figure 7-13) can be seen as one 32-bit register,
RSM. Bit n in RSM (RSn) is an enable/disable control bit for time slot number N. When RSn
is cleared, all the data signals of the enabled receivers are tri-stated during time slot number
N. Data transfers from the receive data register(s) to the receive shift register(s), but the RDF
and ROE flags are not set. Consequently, during a disabled slot, no receiver full interrupt is
generated. The DSP is interrupted only for enabled slots. When RSn is set, the receive
sequence proceeds normally. Data is received during slot number N, and the RDF flag is set.
When the bits in the RSM are set, their setting affects the next frame transmission. The frame
being transmitted is not affected by the new RSM setting. If the RSM is read, it shows the
current setting.
When RSMA or RSMB is read by the internal data bus, the register contents occupy the two
low-order bytes of the data bus, and the high-order byte is filled by 0.
After a hardware RESET signal or a software RESET instruction, the RSM register is reset to
$FFFFFFFF, enabling all 32 time slots for data transmission.
23 22 21 20 19 18 17 16 15 14 13 12
RS15 RS14 RS13 RS12
11 10 9 8 7 6 5 4 3 2 1 0
RS11 RS10 RS9 RS8 RS7 RS6 RS5 RS4 RS3 RS2 RS1 RS0
—Reserved bit; read as 0; write to 0 0 for future compatibility.
(ESSI0 X:$FFFFB2, ESSI1 X:$FFFFA2)
Figure 7-16. ESSI Receive Slot Mask Register A (RSMA)
23 22 21 20 19 18 17 16 15 14 13 12
RS31 RS30 RS29 RS28
11 10 9 8 7 6 5 4 3 2 1 0
RS27 RS26 RS25 RS24 RS23 RS22 RS21 RS20 RS19 RS18 RS17 RS16
–Reserved. Read as zero. Write with zero for future compatibility.
(ESSI0 X:$FFFFB1, ESSI1 X:$FFFFA1)
Figure 7-17. ESSI Receive Slot Mask Register B (RSMB)