DS2480B+ Maxim Integrated Products, DS2480B+ Datasheet - Page 8

• Manufacturer Part Number: DS2480B+
• Description: IC LINE DRVR W/SENSOR 1-W 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Line Driver, Transmitterr

Specifications of DS2480B+

• Number Of Drivers/receivers: 1/0
• Protocol: RS232
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

of the pulse command is arming and disarming a strong pullup after every subsequent byte in Data Mode.
The arm/disarm function is controlled by bit 1 of the command code. Bit 4 determines whether the device
will generate a strong pullup to 5V or a 12V programming pulse. The table below summarizes these
options.
The strong pullup to 5V is required to program EEPROM devices or to operate special function devices
that require a higher current for a limited time after having received a “go and convert” command.
Therefore, and because it significantly reduces the effective data throughput on the 1-Wire bus, the strong
pullup is disarmed most of the time. Although arming or disarming is simultaneously possible while
generating a programming pulse, this is not recommended since it is likely to destroy the DS2480B if
non-EPROM devices are connected to the 1-Wire bus.
The duration of the strong pullup or programming pulse is determined by configuration parameters and
ranges from a few microseconds up to unlimited (see Configuration Commands section). However,
unlimited duration is not allowed in conjunction with arming the strong pullup after every byte. As long
as the DS2480B is in Command Mode the host may terminate a strong pullup or programming pulse
prematurely at any time by sending the command code F1h.
The response byte is generated as soon as the strong pullup or programming pulse is over (either because
the predefined time has elapsed, the high current demand is over, or due to termination by the host). The
response byte mainly returns the command code as sent by the host, but the 2 least significant bits are
undefined.
If the strong pullup is armed and the device is in Data Mode, the end of the strong pullup will be signaled
as code F6h if the most significant bit of the preceding data byte on the 1-Wire bus is a 1 and 76h
otherwise. The host will see this response byte in addition to the response on the data byte sent (see also
Waveforms section later in this document).
SEARCH ACCELERATOR INTRODUCTION
The Search Accelerator is a logic block inside the DS2480B that allows using the Search ROM function
very efficiently under modern operating systems. Without the DS2480B all 1-Wire port adapters have to
involve the computer’s CPU for every single time slot or pulse to be generated on the 1-Wire bus.
Under some operating systems it may take several milliseconds or more to get the first time slot generated
on the 1-Wire bus when sending commands to the UART. Every subsequent time slot will be generated in
much less time, since the computer simply sends out “streams”—a long chain of bytes. This works
reasonably well when reading or writing large blocks of data.
Searching the 1-Wire bus to identify all ROM IDs of the devices connected, however, requires reading 2
bits, making a decision and then writing a bit. This procedure is to be repeated 64 times to identify and
address a single device. With the overhead of modern operating systems this fairly simple process takes a
lot of time, reducing the discovery rate of devices on the 1-Wire bus. To solve this problem the Search
Accelerator was developed.
BIT 4
0
1
0
1
BIT 1
0
0
1
1
Strong pullup to 5V and disarm
12V programming pulse and disarm
Strong pullup to 5V and arm
12V programming pulse and arm
FUNCTION
8 of 32