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1-Wire Bus Master Interface
Copyright © 12/13/06 Marvell
CONFIDENTIAL
Doc. No. MV-TBD-00 Rev. A
December 13, 2006
Document Classification: Proprietary Information
Page 285
Not approved by Document Control. For review only.
1-Wire bus must not be made as the byte in the receive buffer is overwritten by the next received byte resulting in
lost data. Interrupt flags are explained in more detail in
Section 10.4.3, “1-Wire Interrupt Register (W1INTR)”
. Write and read operations are detailed in
and
Figure 9-5
.
10.3.3
I/O Signaling
The 1-Wire bus requires strict signaling protocols to ensure data integrity. The four protocols used by the 1-Wire
bus master interface controller are as follows:
•
Initialization sequence (reset pulse followed by presence pulse)
•
Write 0
•
Write 1
•
Read data
The master initiates all of these types of signaling except the presence pulse.
10.3.3.1
Initialization Sequence
shows the initialization sequence required to begin any communication with the bus slave. See the
PXA300 Processor and PXA310 Processor Electrical, Mechanical, and Thermal Specification for detailed
timing information. The 1-Wire bus master controller transmits a reset pulse. The 1-Wire bus line is then pulled
high by the external pullup resistor. After detecting the rising edge on the ONE_WIRE pin, the slave waits for a
required amount of delay time and then transmits the presence pulse. The master samples the bus during the
presence pulse after the slave responds to test for a valid-presence pulse. The result of this sample is stored in the
PDR bit of the 1-Wire Interrupt register, W1INTR[PDR]. The reset time slot ends a specified amount of time
after the master releases the bus.
Figure 10-2. 1-Wire Initialization Sequence (Reset and Presence Pulses)
10.3.3.2
Write Time Slots
A write time slot is initiated when the 1-Wire bus master drives the 1-Wire bus line from a logic-high (inactive)
level to a logic-low level. The 1-Wire bus master generates a write-1 time slot by releasing the bus line after the
required amount of logic-low time for a write-1 allowing the bus line to pull up to a logic-high level. The 1-Wire
bus master generates a write-0 time slot by holding the bus line low for the required amount of logic-low time. A
VCC
GND
ONE_WIRE
Master samples bus
Presence pulse
Reset time slot ends
Reset pulse
LINE TYPE LEGEND:
Delay
Slave device active low
1-Wire Master active low
Resistor pullup