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HDQ and 1-Wire Protocols
7.2
1-Wire Mode (SDQ)
206
Serial Interfaces
This section highlights the primary differences between the HDQ and the
1-Wire protocols.
In the 1-Wire mode, the firmware must send an initialization pulse to the
multiple slaves that can be connected on the interface. If any slave is present,
the slave responds with a presence pulse.
The initialization pulse is sent by setting the appropriate bit in the control and
status register. A presence detect is indicated in the appropriate bit of the
register. If no presence is received, a time-out bit is set in the status register.
The initialization bit is cleared at the end of the initialization pulse. Also, the
presence detect and the time-out bits are cleared at the end of the initialization
pulse, if a presence detect is received. The time-out bit has no other
significance in this mode; that is, unlike in HDQ mode, it is always cleared
during a read operation.
1-Wire mode is a bit-by-bit protocol for a read. Unlike HDQ, which sends eight
bits of data on a read, the slave must be clocked by the host in 1-Wire protocol
for each bit. At the end of the command/address byte, the line is pulled high
and the host creates a low-going edge to initiate a bit read from the slave. The
host then pulls the line high, and the slave either pulls the line low to indicate
a 0 or does not drive the line to indicate a 1. The host repeats the operation
for the next bit that need to be read.
The first bit that is received is the LSB and the last bit is the MSB in the RX data
register.
An interrupt condition indicates either a TX complete, RX complete, or time-out
condition. The read of the interrupt status register clears all of the interrupt
conditions. Only one interrupt signal is sent to the microcontroller, and only an
overall mask bit exists for the enabling and disabling of the interrupt. The
interrupt conditions cannot be individually masked.
The programmer must perform the following sequence for the reads and writes
to the slave:
Write operation:
1) Write the ID, command, or data value to the TX write register.
2) Write 0 to the R/W bit of the control and status register to indicate a write.
3) Write 1 to the go bit of the control and status register to start the actual
transmit. This step and the above step can be done at the same time.
SPRU760B
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