Linx HumPRC Series Data Manual page 21

The Command Data Interface
The HumPRC Series transceiver has a serial Command Data Interface
TM
(CDI) that is used to configure and control the transceiver through
software commands. This interface consists of a standard UART with a
serial command set. The CMD_DATA_IN and CMD_DATA_OUT lines are
the interface to the module's UART. The UART is configured for 1 start
bit, 1 stop bit, 8 data bits, no parity and a serial data rate set by register
UARTBAUD (default 9,600bps).
Configuration settings are stored in two types of memory inside the
module. Volatile memory is quick to access, but it is lost when power is
removed from the module. Non-volatile memory has a limited number of
write cycles, but is retained when power is removed. When a configuration
parameter has both a non-volatile and volatile register, the volatile register
controls the operation unless otherwise stated. The non-volatile register
holds the default value that is loaded into the volatile register on power-up.
Configuration settings are read from non-volatile memory on power up
and saved in volatile memory. The volatile and non-volatile registers have
different address locations, but the same read and write commands. The
two locations can be changed independently.
The general serial command format for the module is:
[FF] [Length] [Command]
The Length byte is the number of bytes in the Command field. The
Command field contains the register address that is to be accessed and,
in the case of a write command, the value to be written. Neither Length nor
Command can contain a 0xFF byte.
Byte values of 128 (0x80) or greater can be sent as a two-byte escape
sequence of the format:
0xFE, [value - 0x80]
For example, the value 0x83 becomes 0xFE, 0x03. The Length count
includes the added escape bytes.
A response is returned for all valid commands. The first response byte is
CMD_ACK (0x06) or CMD_NACK (0x15). Additional bytes may follow, as
determined by the specific command.
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Reading from Registers
A register read command is constructed by placing an escape character
(0xFE) before the register number. The module responds by sending an
ACK (0x06) followed by the register number and register value. The register
value is sent unmodified, so if the register value is 0x83, 0x83 is returned.
If the register number is invalid, the module responds with a NACK (0x15).
The command and response are shown in Figure 28.
HumPRC Series Read From Configuration Register
TM
Command
Header Size Escape Address
0xFF 0x02 0xFE REG
Response
ACK Address Value
0x06 REG V
Command for an Address greater than 128 (0x80)
Header Size Escape Addr1
0xFF 0x03 0xFE 0xFE
Response
ACK Address Value
0x06 REG V
Figure 28: HumPRC TM Series Read from Configuration Register Command and Response
Addr2
REG-80
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