DS2408 Maxim, DS2408 Datasheet - Page 24

• Manufacturer Part Number: DS2408
• Description: The DS2408 is an 8-channel, programmable I/O 1-Wire® chip
• Manufacturer: Maxim

DS2408
1-WIRE SIGNALING
The DS2408 requires strict protocols to ensure data integrity. The protocol consists of four types of
signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One, and
Read-Data. Except for the presence pulse, the bus master initiates all these signals. The DS2408 can
communicate at two different speeds, standard speed, and overdrive speed. If not explicitly set into the
overdrive mode, the DS2408 will communicate at standard speed. While in overdrive mode, the fast
timing applies to all waveforms.
To get from idle to active, the voltage on the 1-Wire line needs to fall from V
below the V
threshold.
PUP
TL
To get from active to idle, the voltage needs to rise from V
past the V
threshold. The V
ILMAX
TH
ILMAX
voltage is relevant for the DS2408 when determining a logical level, not triggering any events.
Figure 13 shows the initialization sequence required to begin any communication with the DS2408. A
Reset Pulse followed by a Presence Pulse indicates the DS2408 is ready to receive data, given the correct
ROM and control function command. If the bus master uses slew-rate control on the falling edge, it must
pull down the line for t
+ t
to compensate for the edge. A t
duration of 480µs or longer will exit
RSTL
F
RSTL
the overdrive mode returning the device to standard speed. If the DS2408 is in overdrive mode and t
RSTL
is no longer than 80µs the device will remain in overdrive mode.
Figure 13. INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES”
After the bus master has released the line it goes into receive mode (RX). The 1-Wire bus is then pulled
to V
via the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the V
PUP
TH
threshold is crossed, the DS2408 waits for t
and then transmits a Presence Pulse by pulling the line
PDH
low for t
. To detect a presence pulse, the master must test the logical state of the 1-Wire line at t
.
PDL
MSP
The t
window must be at least the sum of t
, t
, and t
. Immediately after t
is
RSTH
PDHMAX
PDLMAX
RECMIN
RSTH
expired, the DS2408 is ready for data communication. In a mixed population network, t
should be
RSTH
extended to a minimum of 480µs at standard speed and 48µs at overdrive speed to accommodate other 1-
Wire devices.
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