Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
10-10
Freescale Semiconductor
Serial Host Interface (SHI, SHI_1)
When HFM[1:0] = 00, the filter is bypassed (spikes are not filtered out). This mode is useful when higher
bit-rate transfers are required and the SHI operates in a noise-free environment.
When HFM[1:0] = 01, the very narrow-spike-tolerance filter mode is selected. In this mode the filters
eliminate spikes with durations of up to 10 ns. This mode is useful when very high bit-rate transfers are
required and the SHI operates in a nearly noise-free environment.
When HFM[1:0] = 10, the narrow-spike-tolerance filter mode is selected. In this mode the filters eliminate
spikes with durations of up to 50 ns. This mode is suitable for use in mildly noisy environments and
imposes some limitations on the maximum achievable bit-rate transfer.
When HFM[1:0] = 11, the wide-spike-tolerance filter mode is selected. In this mode the filters eliminate
spikes up to 100 ns. This mode is recommended for use in noisy environments; the bit-rate transfer is
strictly limited. The wide-spike- tolerance filter mode is highly recommended for use in I
2
C bus systems
as it fully conforms to the I
2
C bus specification and improves noise immunity.
NOTE
HFM[1:0] are cleared during hardware reset and software reset.
After changing the filter bits in the HCKR register to a non-bypass mode (HFM[1:0] is not equal to ‘00’),
the programmer should wait at least ten times the tolerable spike width before enabling the SHI (setting
the HEN bit in the HCSR register). Similarly, after changing the HI
2
C bit in the HCSR register or the
CPOL bit in the HCKR register, while the filter mode bits are in a non-bypass mode (HFM[1:0] is not
equal to ‘00’), the programmer should wait at least ten times the tolerable spike width before enabling the
SHI (setting HEN bit in the HCSR register).
10.3.8
SHI Control/Status Register (HCSR)—DSP Side
The HCSR is a 24-bit register that controls the SHI operation and indicates its status. The control bits are
read/write; the status bits are read-only. The HCSR register bits are described in the following sections.
When in the stop state or during individual reset, the HCSR status bits are reset to their hardware-reset
state, while the HCSR control bits are not affected.
10.3.8.1
HCSR Host Enable (HEN)—Bit 0
The read/write control bit HEN, when set, enables the SHI. When HEN is cleared, the SHI is disabled (the
SHI is in the individual reset state). When HEN is cleared, the HCKR and the HCSR control bits are not
Table 10-3. SHI Noise Reduction Filter Mode
HFM1
HFM0
Description
0
0
Bypassed (Disabled)
0
1
Very Narrow Spike Tolerance
1
0
Narrow Spike Tolerance
1
1
Wide Spike Tolerance
Содержание Symphony DSP56724
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