Signed Data Format; Launching Conversions - ST STM32F423 Reference Manual

Digital filter for sigma delta modulators (DFSDM)
Note: In case of filter and integrator bypass (IOSR[7:0]=0, FOSR[9:0]=0), the input data rate
(f
DATAIN_RATE
f
DATAIN_RATE
where f
APB
15.4.14

Signed data format

Each DFSDM input serial channel can be connected to one external Σ∆ modulator. An
external Σ∆ modulator can have 2 differential inputs (positive and negative) which can be
used for a differential or single-ended signal measurement.
A Σ∆ modulator output is always assumed in a signed format (a data stream of zeros and
ones from a Σ∆ modulator represents values -1 and +1).
Signed data format in registers: Data is in a signed format in registers for final output data,
analog watchdog, extremes detector, offset correction. The msb of output data word
represents the sign of value (two's complement format).
15.4.15

Launching conversions

Injected conversions can be launched using the following methods:
•
Software: writing '1' to JSWSTART in the DFSDM_FLTxCR1 register.
• Trigger: JEXTSEL[2:0] selects the trigger signal while JEXTEN activates the trigger
and selects the active edge at the same time (see the DFSDM_FLTxCR1 register).
•
Synchronous with DFSDM_FLT0 if JSYNC=1: for DFSDM_FLTx (x>0), an injected
conversion is automatically launched when in DFSDM_FLT0; the injected conversion is
started by software (JSWSTART=1 in DFSDM_FLT0CR2 register). Each injected
conversion in DFSDM_FLTx (x>0) is always executed according to its local
configuration settings (JSCAN, JCHG, etc.).
If the scan conversion is enabled (bit JSCAN=1) then, each time an injected conversion is
triggered, all of the selected channels in the injected group (JCHG[7:0] bits in
DFSDM_FLTxJCHGR register) are converted sequentially, starting with the lowest channel
(channel 0, if selected).
If the scan conversion is disabled (bit JSCAN=0) then, each time an injected conversion is
triggered, only one of the selected channels in the injected group (JCHG[7:0] bits in
DFSDM_FLTxJCHGR register) is converted and the channel selection is then moved to the
next selected channel. Writing to the JCHG[7:0] bits when JSCAN=0 sets the channel
selection to the lowest selected injected channel.
Only one injected conversion can be ongoing at a given time. Thus, any request to launch
an injected conversion is ignored if another request for an injected conversion has already
been issued but not yet completed.
Regular conversions can be launched using the following methods:
•
Software: by writing '1' to RSWSTART in the DFSDM_FLTxCR1 register.
•
Synchronous with DFSDM_FLT0 if RSYNC=1: for DFSDM_FLTx (x>0), a regular
conversion is automatically launched when in DFSDM_FLT0; a regular conversion is
started by software (RSWSTART=1 in DFSDM_FLT0CR2 register). Each regular
conversion in DFSDM_FLTx (x>0) is always executed according to its local
configuration settings (RCONT, RCH, etc.).
Only one regular conversion can be pending or ongoing at a given time. Thus, any request
to launch a regular conversion is ignored if another request for a regular conversion has
416/1324
) must be limited to be able to read all output data:
≤ f
APB
is the bus frequency to which the DFSDM peripheral is connected.
RM0430 Rev 8
RM0430