Essi control register a (cra) bit definitions -15 – Motorola DSP56301 User Manual
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ESSI Programming Model
Enhanced Synchronous Serial Interface (ESSI)
7
-15
Table 7-3. ESSI Control Register A (CRA) Bit Definitions
Bit Number
Bit Name
Reset Value
Description
23
0
Reserved. Write to 0 for future compatibility.
22
SSC1
0
Select SC1
Controls the functionality of the SC1 signal. If SSC1 is set, the ESSI is
configured in Synchronous mode (the CRB synchronous/asynchronous bit
(SYN) is set), and transmitter 2 is disabled (transmit enable (TE2) = 0), then
the SC1 signal acts as the transmitter 0 driver-enabled signal while the SC1
signal is configured as output (SCD1 = 1). This configuration enables an
external buffer for the transmitter 0 output. If SSC1 is cleared, the ESSI is
configured in Synchronous mode (SYN = 1), and transmitter 2 is disabled
(TE2 = 0), then the SC1 acts as the serial I/O flag while the SC1 signal is
configured as output (SCD1 = 1).
21–19
WL[2–0]
0
Word Length Control
Select the length of the data words transferred via the ESSI. Word lengths of
8-, 12-, 16-, 24-, or 32-bits can be selected. The ESSI data path
programming model in Figure 7-12 and Figure 7-13 shows additional
information on how to select different lengths for data words. The ESSI data
registers are 24 bits long. The ESSI transmits 32-bit words in one of two
ways:
n
by duplicating the last bit 8 times when WL[2–0] = 100
n
by duplicating the first bit 8 times when WL[2–0] = 101.
Note:
When WL[2–0] = 100, the ESSI is designed to duplicate the last bit
of the 24-bit transmission eight times to fill the 32-bit shifter.
Instead, after the 24-bit word is shifted correctly, eight zeros (0s)
are shifted.
ESSI Word Length Selection
WL2
WL1
WL0
Number of Bits/Word
0
0
0
8
0
0
1
12
0
1
0
16
0
1
1
24
1
0
0
32
(valid data in the first 24
bits)
1
0
1
32
(valid data in the last 24
bits)
1
1
0
Reserved
1
1
1
Reserved
Note:
When the ESSI transmits data in On-Demand mode (that is, MOD =
1 in the CRB and DC[4–0]=00000 in the CRA) with WL[2–0] = 100,
the transmission does not work properly. To ensure correct
operation, do not use On-Demand mode with the WL[2–0] = 100
32-bit word length mode.