DSP56303 FREESCALE [Freescale Semiconductor, Inc], DSP56303 Datasheet - Page 146

• Manufacturer Part Number: DSP56303
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Enhanced Synchronous Serial Interface (ESSI)
7-14
Bit Number
21–19
18
17
Table 7-3. ESSI Control Register A (CRA) Bit Definitions (Continued)
Bit Name
WL[2–0]
ALC
Reset Value
0
0
DSP56303 User’s Manual, Rev. 2
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:
• By duplicating the last bit 8 times when WL[2–0] = 100
• By duplicating the first bit 8 times when WL[2–0] = 101.
Note:
Note:
Alignment Control
The ESSI handles 24-bit fractional data. Shorter data words are left-aligned to
the MSB, bit 23. For applications that use 16-bit fractional data, shorter data
words are left-aligned to bit 15. The ALC bit supports shorter data words. If
ALC is set, received words are left-aligned to bit 15 in the receive shift register.
Transmitted words must be left-aligned to bit 15 in the transmit shift register. If
the ALC bit is cleared, received words are left-aligned to bit 23 in the receive
shift register. Transmitted words must be left-aligned to bit 23 in the transmit
shift register.
Note:
Reserved. Write to 0 for future compatibility.
WL2
0
0
0
0
1
1
1
1
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.
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.
If the ALC bit is set, only 8-, 12-, or 16-bit words are used. The use of
24- or 32-bit words leads to unpredictable results.
WL1
0
0
1
1
0
0
1
1
ESSI Word Length Selection
Description
WL0
0
1
0
1
0
1
0
1
(valid data in the first 24
(valid data in the last 24
Number of Bits/Word
Freescale Semiconductor
Reserved
Reserved
bits)
bits)
12
16
24
32
32
8