RFM CCT24 Series Integration Manual Download

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CCT24

radio, protocol formatting must be used unless the data being sent includes addressing information that
the devices connected to the remotes/routers can use to determine the intended destination of the broad-
cast data. Protocol formatting is also required for configuration commands and responses, and sensor I/O
commands and responses. Protocol mode can be used at the base while transparent mode is used at the
remotes. The one caution about protocol mode: the length of a protocol mode message cannot exceed
the

BaseSlotSize

RemoteSlotSize

or the packet will be discarded. Protocol formatting details are

covered in Section 4.

The CCT24 provides two ways to switch between transparent and protocol modes. To enter protocol
mode, the /CFG input Pin 18 can be switched from logic high to low, or the

EnterProtocolMode

command

can be sent. When input Pin 18 is switched from logic low to high, or an

ExitProtocolMode

command is

sent to the primary serial input, the CCT24 will switch to transparent operation. Note that it is possible that
part of the

EnterProtocolMode

command will be sent over the air as transparent data.

When operating in transparent mode, two configuration parameters control when a CCT24 radio will send
the data in its transmit buffer. The

MinPacketLength

parameter sets the minimum number of bytes that

must be present in the transmit buffer to trigger a transmission. The

TxTimeout

parameter sets the maxi-

mum time data in the transmit buffer will be held before transmitting it, even if the number of data bytes is
less than

MinPacketLength

. The default value for

MinPacketLength

parameter is one and the

TxTimeout

parameter is zero, so that any bytes that arrive in the CCT24 transmit buffer will be sent on the next hop.
As discussed in Section 2.8.2, it is useful to set these parameters to values greater than their defaults in
point-to-multipoint systems where some or all the remotes are in transparent mode.

2.4 SPI Port Modes

CCT24 radios can be configured to transmit and receive data through the serial peripheral interface (SPI)
port instead of the primary serial (UART) port. A CCT24 can operate as either an SPI Master or Slave.
Messages routed through the SPI port must be protocol formatted, as described in Section 4. When a
CCT24 is acting as an SPI Slave, all messages are routed through the SPI port. When a CCT24 is acting
as an SPI Master, only data messages are routed through the SPI port; radio configuration commands
and responses are routed through the primary serial (UART) port. A radio configured as an SPI Master
can use a command stored in the

SPI_MasterCmdStr

parameter to interrogate a Slave peripheral for

data to transmit to the base. This is especially useful where periodic I/O reporting is enabled on the
remote. Alternately, the base can send an interrogation command to the radio to fetch peripheral data.
SPI operation is configured with the

SPI_Mode

parameter.

2.5 RF Data Communications

At the beginning of each hop the base transmits a beacon, which always includes a synchronizing signal.
After synchronization is sent, the base will transmit any user data in its transmit buffer, unless in transpar-
ent mode the

MinPacketLength

and/or

TxTimeout

parameters have been set above their default values.

The maximum amount of user data bytes that the base can transmit per hop is limited by the

BaseSlot-

Size

parameter, as discussed in Section 2.8.1. If there is no user data or reception acknowledgements

(ACKs) to be sent on a hop, the base will only transmit the synchronization signal in the beacon.

The operation for remotes and routers is similar to the base, but without a synchronizing signal. The

RemoteSlotSize

parameter indicates the maximum number of user data bytes a remote or router can