DS2482-100_12 MAXIM [Maxim Integrated Products], DS2482-100_12 Datasheet - Page 7

• Manufacturer Part Number: DS2482-100_12
• Description: Single-Channel 1-Wire Master
• Manufacturer: MAXIM [Maxim Integrated Products]

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 DS2482-100 to
the 1-Wire line. See the ΔV
Electrical Characteristics to determine if the internal
strong pullup is sufficient given the current load on the
device.
If SPU is 1, the DS2482-100 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 transistor,
remains conducting, as shown in Figure 3, until one of
three events occurs: the DS2482-100 receives a command
that generates 1-Wire communication (the typical case);
the SPU bit in the Configuration Register is written to 0; or
the DS2482-100 receives the Device Reset command. As
Figure 3. Low-Impedance Pullup Timing
V
CC
0V
_______________________________________________________________________________________
DS2482-100 RESISTIVE PULLUP
PCTLZ
LAST BIT OF 1-Wire WRITE BYTE OR 1-Wire SINGLE BIT FUNCTION
STRPU
Strong Pullup (SPU)
parameter in the
WRITE-ONE CASE
Single-Channel 1-Wire Master
t
SLOT
WRITE-ZERO CASE
DS2482-100 PULLDOWN
long as the strong pullup is active, the PCTLZ output is low.
When the strong pullup ends, the SPU bit is automati-
cally 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 incorrect
reading of the presence pulse and may cause a viola-
tion of the device’s absolute maximum rating.
The 1WS bit determines the timing of any 1-Wire com-
munication generated by the DS2482-100. All 1-Wire
slave devices support standard speed (1WS = 0),
where the transfer of a single bit (t
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
DS2482-100 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 DS2482-100 and any
1-Wire devices on the active 1-Wire line back to stan-
dard speed.
DS2482-100 STRONG PULLUP
1-Wire Speed (1WS)
SLOT
in Figure 3) is
NEXT
TIME SLOT
OR 1-Wire
RESET
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