Single-Channel 1-Wire Master with Sleep Mode
DS482-01
Strong Pullup (SPU)
The SPU bit is used to activate the strong pullup func-
tion prior to a 1-Wire Write Byte or 1-Wire Single Bit
command. Strong pullup is commonly used with 1-Wire
EEPROM devices when copying scratchpad data to the
main memory or when performing an SHA-1 computa-
tion and with parasitically powered temperature sen-
sors or A/D converters. The respective device data
sheets specify the location in the communications pro-
tocol after which the strong pullup should be applied.
The SPU bit must be set immediately prior to issuing
the command that puts the 1-Wire device into the state
where it needs the extra power. The strong pullup uses
the same internal pullup transistor as the active pullup
feature. For cases where the internal strong pullup has
insufficient strength, the PCTLZ pin can be used to con-
trol an external p-channel MOSFET to supply additional
power beyond the drive capability of the DS2482-101 to
Reset command. As long as the strong pullup is active,
the PCTLZ output is low. When the strong pullup ends, the
SPU bit is automatically reset to 0. Using the strong pullup
feature does not change the state of the APU bit in the
Configuration Register. Note: Strong pullup also affects
the 1-Wire Reset command. If enabled, it can cause incor-
rect reading of the presence pulse and may cause a vio-
lation of the device’s absolute maximum rating.
1-Wire Speed (1WS)
The 1WS bit determines the timing of any 1-Wire com-
munication generated by the DS2482-101. All 1-Wire
slave devices support standard speed (1WS = 0),
where the transfer of a single bit (t
in Figure 3) is
SLOT
completed within 65µs. Many 1-Wire devices can also
communicate at a higher data rate, called overdrive
speed. To change from standard to overdrive speed, a
1-Wire device needs to receive an Overdrive-Skip ROM
or Overdrive-Match ROM command, as explained in
the 1-Wire device data sheets. The change in speed
occurs immediately after the 1-Wire device has
received the speed-changing command code. The
DS2482-101 must take part in this speed change to
stay synchronized. This is accomplished by writing to
the Configuration Register with the 1WS bit as 1 imme-
diately after the 1-Wire Byte command that changes the
speed of a 1-Wire device. Writing to the Configuration
Register with the 1WS bit as 0, followed by a 1-Wire
Reset command, changes the DS2482-101 and any
1-Wire devices on the active 1-Wire line back to stan-
dard speed.
the 1-Wire line. See the ΔV
parameter in the
STRPU
Electrical Characteristics to determine if the internal
strong pullup is sufficient given the current load on the
device.
If SPU is 1, the DS2482-101 treats the rising edge of the
time slot in which the strong pullup starts as if the active
pullup was activated. However, in contrast to the active
pullup, the strong pullup, i.e., the internal pullup transis-
tor, remains conducting, as shown in Figure 3, until one
of three events occurs: the DS2482-101 receives a
command that generates 1-Wire communication (the
typical case); the SPU bit in the Configuration Register
is written to 0; or the DS2482-101 receives the Device
LAST BIT OF 1-Wire WRITE BYTE OR 1-Wire SINGLE BIT FUNCTION
WRITE-ONE CASE
V
CC
NEXT
TIME SLOT
OR 1-Wire
RESET
WRITE-ZERO CASE
0V
t
SLOT
PCTLZ
DS2482-101 RESISTIVE PULLUP
DS2482-101 PULLDOWN
DS2482-101 STRONG PULLUP
Figure 3. Low-Impedance Pullup Timing
_______________________________________________________________________________________
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