DS2480B Maxim Integrated Products, DS2480B Datasheet - Page 20

• 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: Contains lead / RoHS non-compliant

DS2480B
PULSE WAVEFORM, ARMED
As explained in the Communication Commands section, bit 1 of the Pulse command allows the arming of
a strong pullup to 5V if the bit is set to 1. If the strong pullup is armed and the device is switched to Data
Mode, there will be a strong pullup immediately following every byte on the 1-Wire bus. This mode is
implemented to provide extra energy when writing to EEPROM devices or to do a temperature
conversion with the DS1920 temperature iButton, for example. These devices need a strong pullup
immediately after the power-consuming activity has been initiated by a command code.
To arm the strong pullup, one usually generates a “dummy” pulse with bit 1 being 1 while the device is in
Command Mode. To save time, the dummy pulse may immediately be terminated by sending the
Termination command, code F1h. Then one switches to Data Mode and sends a command code that
makes one or more slaves on the 1-Wire bus require extra energy. After the command execution is
finished, one switches back to Command Mode and disarms the strong pullup by generating another
dummy pulse. A complete temperature conversion sequence that shows the use of the armed pulse is
included in the Software Driver Examples section .
Figure 8. STRONG PULLUP TO 5V, ARMED, PREDEFINED DURATION
th
Figures 8 shows the timing of the strong pullup in Data Mode. At t
the 8
time slot of the byte sent to the
1
1-Wire bus is completed. Without any delay the DS2480B now activates the strong pullup and
simultaneously starts sending the data response byte to the host. At t
the strong pullup ends and the
2
DS2480B sends a pulse response byte to the host. The idle time between t
and t
is comprised of the time
2
3
to transmit the pulse response byte, plus the response time of the host plus the time to transmit the
command and/or data to generate the next time slot. Since in Data Mode the Pulse Termination command
is not applicable, the duration of the strong pullup must be limited. See Table 4, parameter 011 (Strong
Pullup Duration) for details.
Dynamic duration is permissible in conjunction with the armed pulse function. However, the load sensor
does not have the sensitivity required for detecting when the high current demand of a single 1-Wire
temperature sensor or EEPROM device ends. Since the duration of the high current demand of such
devices depends on temperature and is slightly different for every individual device, even with multiple
EEPROMs or temperature sensors operating simultaneously, dynamic duration should not be used.
Infinite duration, if accidentally selected, will require a power-on or master reset cycle to get the
DS2480B back to communicating with the host.
20 of 31