SA9904APA Ver la hoja de datos (PDF) - South African Micro Electronic Systems
Número de pieza
componentes Descripción
Fabricante
SA9904APA Datasheet PDF : 12 Pages
| |||
SA9904A
sames
DATA FORMAT
Figure 5 shows the SPI waveforms. After the least significant
digit of the address has been entered on the rising edge of
SCK, the output DO goes low with the falling edge of SCK.
Each subsequent falling edge transition on the SCK pin will
validate the next data bit on the DO pin.
The content of each register consists of 24 bits of data. The
MSB is shifted out first.
SCK
t3
t4
DI
t2
t5
DO
t1
CS
DR-01545
Parameter Description
Min Max
t1 SCK rising edge to DO valid 625ns 1.160µs
t3 SCK min high time
625ns
t4 SCK min low time
625ns
t2 Setup time for DI and CS
before the rising edge of SCK 20ns
t5 DI hold time
625ns
Figure 6: SPI Timing diagrams
ACTIVE AND REACTIVE REGISTER VALUES
The active and reactive registers are 24 bit up/down counters,
that increment or decrement at a rate of 320k samples per
second at rated conditions. The register values will increment
for positive energy flow and decrement for negative energy
flow as indicated in figure 7. The active and reactive registers
are not reset after access, so in order to determine the correct
register value, the previous value read must be subtracted
from the current reading. The data read from the registers
represents the active or reactive power integrated over time.
The increase or decrease between readings represent the
measured energy consumption.
Register wrap around
Positive energy flow
Register values
H7FFFFF H800000
HFFFFFF
0 ................ (8388607) (8388608) ................ (16777215)
Negative energy flow
DR-01590
Register wrap around
Figure 7: Register increment / decrement showing the
register wrap around
At rated conditions, the active and reactive registers will wrap
around every 26 seconds. The micro controller program needs
to take this condition into account when calculating the
difference between register values.
As an example lets assume that with a constant load
connected, the delta value (delta value = present register -
previous register value) is 22260. Because of the constant
load, the delta value should always be 22260 every time the
register is read and the previous value subtracted (assuming
the same time period between reads). However this will not be
true when a wrap around occurs, as the following example will
demonstrate:
Description
Valiable Decimal
Hex
Present register value new_val 16767215 0x00FFD8EF
Previous register value old_val 16744955 0x00FF81FB
new_val - old_val = delta_val 22260 0x000056F4
The register now wraps around so after the next read
the values are as follows:
Present register value new_val
12259 0x00002FE4
Previous register value old_val 16767215 0x00FFD8EF
new_val - old_val = delta_val -16754955 0x00FFA90B
Computing this delta value will result in incorrect calculations.
http://www.sames.co.za
7/12
Share Link: 