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CC112X/CC1175
SWRU295C
Page 52 of 108
7.7.2
Transparent Serial Mode
CC112X
does not do any timing recovery and just outputs the hard limited baseband signal. In
transparent serial mode the data rate programming does not affect operation. When transparent
mode is enabled, the device is set up to resemble a legacy purely analog front end device with
baseband output to support legacy pulse position modulation, PWM modulated signals etc. In
transparent mode the signal is digitally demodulated and output on GPIO pins through a
programmable interpolation filter (
). The interpolation filter is used
to eliminate jitter on the baseband signal. This is useful when using external DSP demodulators as
jitter introduce noise in the demodulation process. The rate on the GPIO is ((4 x receiver bandwidth) x
interpolation factor).
When using transparent serial mode make sure the interfacing MCU/DSP does proper oversampling.
In transparent serial mode, several of the support mechanisms for the MCU that are included in
CC112X
will be disabled, such as packet handling hardware, buffering in the FIFO, and so on.
Preamble and sync word insertion/detection is not supported in transparent serial mode.
For TX operation, the GPIO0 pin is explicitly used as serial data input. This is automatically done
when in TX. In order to avoid internal I/O conflict, GPIO0 should be defined as tri-state. GPIO0 will be
automatically tri-stated in TX if the GPIO0 is defined as serial clock or serial data output
(
IOCFG0.GPIO0_CFG = 8
or
9
). If this is not the case, GPIO0 must be manually tri-stated by
setting
(48).
Data output can be observed on GPIO0/1/2/3. This is set by the
IOCFGx.GPIOx_CFG
fields.
In addition to set
PKT_CFG2.PKT_FORMAT = 11b
, the following register fields must be set:
MDMCFG1.FIFO_EN = 0
MDMCFG0.TRANSPARENT_MODE_EN = 1
IOCFGx.GPIOx_CFG = 001001b
. Only necessary for RX mode)
SERIAL_STATUS.IOC_SYNC_PINS_EN = 1
(Only necessary for TX mode)