UG-1098
ADE9000 Technical Reference Manual
Rev. 0 | Page 36 of 86
WAVEFORM BUFFER
has a waveform buffer comprised of 2048, 32-bit
memory locations with addresses from 0x800 to 0xFFF. This
memory can be filled with samples from the sinc4 or sinc4 + IIR
LPF, current and voltage waveform samples processed by the
digital signal processor or resampled waveforms.
Resampled waveforms make it easy to perform harmonic analysis
in an external processor, which can use the 16-bit, 128 points per
line cycle samples directly in a FFT, without having to perform
any windowing functions or changing the FFT coefficients
function of line period.
The data in the waveform buffer can come from four locations
in the signal chain:
Sinc4 outputs, xI_SINC_DAT, xV_SINC_DAT provided at
32 ksps update rate
Sinc4 + IIR LPF output, xI_LPF_DAT, xV_LPF_DAT
provided at 8 ksps update rate
Current and voltage channel waveforms processed by the
DSP (xI_PCF, xV_PCF) provided at 8 ksps update rate
Resampled waveforms with 128 points per line cycle
processed by the DSP; data rate varies with line period
Filling and accessing of the waveform buffer depends on which
type of data is being filled in the buffer. The waveforms with a
fixed data rate, 32 ksps or 8 ksps, are referred to as fixed data
rate waveforms. Refer to the corresponding section to
understand what modes and access are available for resampled
waveforms vs. fixed data rate waveforms.
The waveform buffer samples can be accessed using the SPI
burst read functionality so that multiple samples can be read
using only one SPI command header (see the Burst Read
Waveform Buffer Samples from SPI section).
FIXED DATA RATE WAVEFORMS
Fixed data rate waveforms from the signal chain can be stored
into the waveform buffer from the places shown in Table 22.
Table 22. Fixed Data Rate Waveform Sources
Source
WFB_CFG.
WF_SRC
Data
Rate
32-Bit Data
Format
Sinc4 Outputs
0
32 ksps
24 bits, shifted left
by 4 bits and sign
extended to 32 bits
Sinc4 + IIR LPF
Output
2 8
ksps
24 bits, shifted left
by 4 bits and sign
extended to 32 bits
Waveforms
Processed by
the DSP (xI_PCF,
xV_PCF)
3
8 ksps
5.27 format
The 24-bit sinc4 and sinc4 + IIR LPF data is stored as 32-bit in
the waveform buffer by shifting by left by 4 bits and sign
extending, as shown in Table 23.
Table 23. 24-Bit Sinc4 and Sinc4 + IIR LPF Data
Bits[31:28] Bits[27:4] Bits[3:0]
SE ADC_DATA[23:0]
0000
Table 22 indicates the WFB_SRC selection for each fixed data
rate waveform source. Each fixed data rate sample is 32-bits;
however, the data format varies between the three sources, as
shown in Table 22. When the waveform buffer is enabled, the
data from all seven channels is stored into the buffer. One
sample set consists of one sample per channel, seven samples
total, which are taken at the same point in time.
Figure 49 shows how the fixed data rate samples are stored into
the buffer. Every sample set is separated in the memory from
the adjacent one by the use of spare cells, which do not contain
any sample data, as shown in Figure 49. In this way, every eighth
32-bit memory location in the buffer is reserved as a spare cell.
If the seventh channel is disabled, with the WF_IN_EN bit in
the WFB_CFG register equal to 0, the IN sample locations are
treated as spare cells as well.
0 xFFF
0
31
IN, IF WFB_CFG.WF_IN_EN = 1
SPARE CELL, IF WFB_CFG.WF_IN_EN = 0
SPARE CELL
IN
0x807
0x806
0x805
0x804
0x803
0x802
0x801
0x800
VC
IC
IN
VC
IC
VB
IB
VA
IA
15523-
049
Figure 49. Fixed Data Rate Waveform Sample Storage
There are 256 (2048/8) sample sets that can be stored in the
buffer. In the
, the sinc4 outputs at 32 ksps, so the
buffer can contain (256/32000) = 8 ms of data from the sinc4.
The sinc4 + IIR LPF samples and DSP processed xI_PCF and
xV_PCF waveform samples are filled at 8 kHz, and the buffer
can contain 32 ms (256/8000) of this data.
When used with fixed data rate samples, the waveform buffer is
divided into 16 pages, Page 0 to Page 15. Each page contains
128, 32-bit memory locations. Figure 50 illustrates this
arrangement.
