General
Review and verify the following for the custom
schematic design:
- Reviewed above "Common checklist for all sections" section of the
user's guide.
- MCASP interface configuration and connections.
- Series resistor provision for clock output and placement.
- Series resistors provision for the interface signals near to the
source.
- Connection of parallel pulls for clock and data.
- Connection of IO supply for IO group and attached device IO supply.
- Interface performance (speed, data throughput, communication errors) and
signal integrity related concerns.
- Parallel pull for processor or attached IOs.
- Connection of MCASP signals when connected to multiple attached
devices.
- Fail-safe operation of MCASP interface.
Schematic Review
Follow the below list for the custom
schematic design:
- MCASP interface configuration and recommended connections (including
IOSET).
- Series resistor (22Ω) added to the clock output signals (transmit bit clock,
frame sync) near to the processor clock output pin (used for retiming).
- Provision for series resistors added (optional) for the interface signals
(to isolate for testing or to control possible signal reflections).
- Pulldown (10kΩ) provision for the MCASP clock (close to attached device
clock input pin) to hold the attached device in low state (there are cases
where the clock is stopped or paused in a low logic state and the pulldown
option is consistent with this logic state) for all IOs configured for MCASP
interfaces.
- Supply rails connected to the IO supply for IO group VDDSHVx referenced to
(powered by) MCASP peripherals and attached devices IO supply are sourced
from the same supply and follow the ROC.
- Pullup referenced to (powered by) the processor VDDSHVx for corresponding
MCASP instance and signals.
- Provide provision for
external pullups for MCASP interface (Transmit or Receive) close to attached
devices. The recommendation is to add pulls to the processor and the
attached device signals (data interface - data in, data out) that can float
(to prevent the attached device inputs from floating until driven by the
host). Pullup values used (10kΩ or 47kΩ).
- Interface performance (speed, data throughput, communication errors) and
signal integrity related concerns have been analyzed (simulated) when
connecting to multiple attached devices.
- Connection of MCASP signals when connected to multiple attached devices.
Follow general design guidelines to minimize stubs.
- Parallel pull added for the processor or attached device IOs that can
float.
- MCASP interface signals are not fail-safe. The recommendation is to apply
the inputs only after the processor supply ramps.
Additional
- The recommendation is to verify fail-safe
operation when connected to external signals. Applying an external input signal
to the processor MCASP inputs before processor supply ramps can cause voltage
feed and can affect the custom board functions.
- Connecting Two (x2) or more devices (common clock
connection, different data signals connection, working simultaneously) to MCASP
interface is supported. The recommendation is to follow good or recommended
layout practices when routing the bit clock (transmit bit clock and receive bit
clock). Perform simulations using IBIS model. The x2 devices (Example: Codec and
amplifier) are recommended to be running with the same format (TDM/I2S/etc) and
Codec and amplifier are recommended to be running with the same format
(TDM/I2S/etc) and word size setup are synchronized with the bit clock and frame
Sync.
- External ESD protection when the
interface signals are connected directly to external inputs.