FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
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3. D7*:D0* relate to the previous 8 bits (last command word) of data that was previously shifted into the device.
4. OD7:OD0 relate to the firstI 8G bitRs Eof 4obrd.ered fLauT lItPaLnd status data outSof thCeOdeviMce.
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U N I C A T I O N
Figure 11. Multiple 8-Bit Word SPI Communication
Table 10, summarizes the SI registers. The registers are
addressed via D6:D4 of the incoming SPI word (Table 9).
SERIAL INPUT COMMUNICATION
SPI communication is accomplished using 8-bit
messages. A message is transmitted by the MCU starting
with the MSB, D7, and ending with the LSB, D0 (Table 9).
Each incoming command message on the SI pin can be
interpreted using the following bit assignments: the MSB (D7)
is the watchdog bit and in some cases a register address bit;
the next three bits, D6:D4, are used to select the command
register; and the remaining four bits, D3:D0, are used to
configure and control the output and its protection features.
Table 9. SI Message Bit Assignment
Bit Sig SI Msg Bit
Message Bit Description
Watchdog in: toggled to satisfy watchdog
requirements; also used as a register
address bit.
MSB
D7
Register address bits.
D6:D4
D3:D1
Multiple messages can be transmitted in succession to
accommodate those applications where daisy chaining is
desirable or to confirm transmitted data as long as the
messages are all multiples of eight bits. Any attempt made to
latch in a message that is not eight bits will be ignored.
Used to configure the inputs, outputs, and
the device protection features and SO
status content.
Used to configure the inputs, outputs, and
the device protection features and SO
status content.
LSB
D0
The 33982 has defined registers, which are used to
configure the device and to control the state of the output.
33982
Analog Integrated Circuit Device Data
Freescale Semiconductor
23
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