DS2482S-800 Maxim Integrated Products, Inc., DS2482S-800 Datasheet - Page 7

• Manufacturer Part Number: DS2482S-800
• Description: Eight-channel 1-wire Master
• Manufacturer: Maxim Integrated Products, Inc.

Presence Pulse Masking (PPM)
The PPM bit controls whether the DS2482 will mask the leading edge (falling) of presence pulses. When PPM = 0,
masking is disabled. Presence pulse masking applies only to standard 1-Wire speed (1WS = 0); this bit has no
function if 1WS = 1 (Overdrive speed). Presence pulse masking can improve the performance of large 1-Wire
networks since it prevents the fast falling edge of a presence pulse generated by a 1-Wire slave device from
propagating through the network and getting reflected. Reflections can cause glitches in the network that in turn
may cause slave devices to lose synchronization with the 1-Wire master.
Figure 3 shows the timing references for the PPM. If enabled (PPM = 1), the DS2482 begins pulling the 1-Wire line
low at t
will be pulling the 1-Wire line low. The falling edge of the presence pulse mask is slew rate controlled.
Figure 3. Presence Pulse Masking
Strong Pullup (SPU)
The SPU bit controls whether the DS2482 applies a low-impedance pullup to V
bit of either a 1-Wire Write Byte command or after a 1-Wire Single Bit command has completed. The strong
pullup feature is commonly used with 1-Wire EEPROM devices when copying scratchpad data to the main memory
or when performing a SHA-1 computation, and with parasitically powered temperature sensors or A-to-D
converters. The respective device data sheets specify the location in the communications protocol after which the
strong pullup should be applied. The SPU bit in the configuration register of the DS2482 must be set immediately
prior to issuing the command that puts the 1-Wire device into the state where it needs the extra power.
If SPU is 1, the DS2482 applies active pullup to the rising edge of the time slot in which the strong pullup starts,
regardless of the APU bit setting. However, in contrast to setting APU = 1 for active pullup, the low-impedance
pullup will not end after t
until: a) the next 1-Wire communication command (the typical case), b) by writing to the Configuration Register with
the SPU bit being 0 (alternative), or c) by issuing the Device Reset command. Additionally, when the pullup ends,
the SPU bit is automatically reset to 0. Using the strong pullup does not change the state of the APU bit in the
Configuration Register.
PPM1
after the reset low time t
V
0V
CC
APUOT
Pull-up
is expired. Instead, as shown in Figure 4, the low-impedance pullup remains active
RSTL
RESET PULSE
t
RSTL
is expired. The pulldown ends at t
APU con-
trolled edge
DS2482 Pull-down
DS2482 pull-down with PPM = 1; Standard speed only
7 of 22
t
PPM1
t
PPM2
PRESENCE PULSE
PPM2
t
, at which a 1-Wire slave, if present,
RSTH
CC
on the 1-Wire line after the last
Resistive
pull-up
1-W Slave Pull-down