WT21-A-HCI Datasheet, PDF (18/54 Pages) List of Unclassifed Manufacturers – Copyright © 2000-2010 Bluegiga Technologies

Figure 5: SPI Write Operation
5.2.2 Reading from the Device
Reading from WT21 is similar to writing to it. An 8-bit read command (00000011) is sent first
(C [7:0]), followed by the address of the location to be read (A[15:0]). WT21 then outputs on
SPI_MISO a check word during T[15:0] followed by the 16-bit contents of the addressed
location during bits D[15:0].
The check word is composed of {command, address [15:8]}. The check word may be used to
confirm a read operation to a memory location. This overcomes the problems encountered with
typical serial peripheral interface slaves, whereby it is impossible to determine whether the data
returned by a read operation is valid data or the result of the slave device not responding.
If SPI_CS# is kept low, data from consecutive locations is read out on SPI_MISO for each
subsequent 16 clocks, until the transaction terminates when SPI_CS# is taken high.
Figure 6: SPI Read Operation
5.2.3 Multi-Slave Operation
WT21 should not be connected in a multi-slave arrangement by simple parallel connection of
slave MISO lines. When WT21 is deselected (SPI_CS# = 1), the SPI_MISO line does not float.
Instead, WT21 outputs 0 if the processor is running or 1 if it is stopped.
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