SIGNALCORE SC5511A Operating & Programming Manual page 45

The data return is invalid for most transfers except for those registers querying for data from the
device. See Reading the SPI Bus section below for more information on retrieving data from the device.
Figure 5 shows the contents of a single 3 byte SPI command written to the device. The Setting the
SC5511A: Configuration Registers section provides information on the number of data bytes and their
contents for an associated register. There is a minimum of 1 data byte for each register even if the data
contents are "zeros".
23
Register Address
Figure 5. Single 3 byte transfer buffer.
Reading the SPI Bus
Data is simultaneously read back during a SPI transfer cycle. Requested data from a prior command is
available on the device SPI output buffers, and these are transferred back to the user host via the SDO
pin. To obtain valid requested data would require querying the SERIAL_OUT_BUFFER, which
requires 6 bytes of clock cycles; 1 byte for the device register (0x26) and 5 empty bytes (MOSI) to
clock out the returned data (MISO). An example of reading the RF parameters (list_start_freq) from
the device is shown in Figure 6.
Request for List-Start-
GET_RF_PARAMETERS
In the above example, valid data is present in the last 5 bytes - byte 4 down to byte 0, where byte 4 is
the most significant byte. Table 46 shows the valid data bytes associated with each of the querying
registers, while Table 47 shows the valid bytes associated with the requested contents of the register.
Table 46. Valid returned data bytes.
Register Name (Address)
GET_RF_PARAMETERS
GET_TEMPERATURE
GET_DEVICE_STATUS
SC5511A User Manual
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0x01
0x20 0x26
Invalid Invalid Invalid
Frequency from the
register
Figure 6. Reading queried data.
Register Code (Hex)
0x20
0x21
0x22
Byte 1
0x00 0x00 0x00
Byte4 Byte3 Byte2
Clock the data out with 5 byte write to register 0x26
Byte 4 Byte 3 Byte 2
valid valid valid
valid valid valid
valid valid valid
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7
Byte 0
0x00 0x00
Byte1 Byte0
Byte 1 Byte 0
valid valid
valid invalid
valid invalid
0
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