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CC112X/CC1175
SWRU295C
Page 51 of 108
7.7
Transparent and Synchronous Serial Operation
Several features and modes of operation have been included in the
CC112X
to provide backward
compatibility with legacy systems that cannot be supported by the built in packet handling
functionality. For new systems, it is recommended to use the built-in packet handling features, as they
give more robust communication, significantly offload the microcontroller, and simplify software
development.
Serial mode is only supported for 2‟ary modulations formats.
There are two serial modes and they are described in the two following sections.
7.7.1
Synchronous Serial Mode
In the synchronous serial mode, data is transferred on a two-wire serial interface. The
CC112X
provides
a clock (
(8)) that is used to set up new data on the data input
line or sample data on the data output line. Data timing recovery is done automatically. The data pin is
updated on the falling edge of the clock pin at the programmed data rate. Sync word
insertion/detection may or may not be active, depending on the sync mode. If sync word detection is
enabled in RX mode (
) will not be
output on the GPIO before a sync word is found. When
transmit a minimum of 4 bytes preamble.
Define a GPIO pin to be serial data clock for both TX and RX operation. For RX operation, another
GPIO pin has to be defined as serial data output (
(9)).
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).
In synchronous serial mode the TX data must be set up on the falling edge of the data clock output
from
CC112X
.
In addition to set
PKT_CFG2.PKT_FORMAT = 01b
, the following register fields must be set:
MDMCFG1.FIFO_EN = 0
MDMCFG0.TRANSPARENT_MODE_EN = 0
IOCFGx.GPIOx_CFG = 001001b
. Only necessary for RX mode)
SERIAL_STATUS.IOC_SYNC_PINS_EN = 1
(Only necessary for TX mode)
PREAMBLE_CFG1.NUM_PREAMBLE = 000
Synchronous serial mode is often used in applications needing to be backward compatible, and sync
detection is disabled (
) since the format of the sync word often do
not match the supported sync word format. Best radio performance is however achieved when
. In cases where the packet has a preamble but not a sync word that matches
the sync format supported by the
CC112X
, the radio can simply use the preamble as a sync word.
Consider the case where a receiver wants to receive packets with 3 different addresses but no
common sync word:
Packet 1: 0xAA, 0xAA, 0xAA, 0xAA,
Address1
, Data0, Data 1, Data 2, …
Packet 1: 0xAA, 0xAA, 0xAA, 0xAA,
Address2
, Data0, Data 1, Data 2, …
Packet 1: 0xAA, 0xAA, 0xAA, 0xAA,
Address3
, Data0, Data 1, Data 2, …
By setting
and
a sync word is
detected somewhere within the preamble and the serial clock will be output on a GPIO when
is asserted. Now the MCU can manually start searching for the 3 different addresses.