DS2480 Dallas Semiconducotr, DS2480 Datasheet - Page 17

• Manufacturer Part Number: DS2480
• Description: Serial 1.Wire Line Driver
• Manufacturer: Dallas Semiconducotr

PULSE WAVE FORM, ARMED
As explained in section Communication Commands, bit
1 of the pulse command allows the arming of a strong
pull–up to 5V if the bit is set to 1. If the strong pull–up is
armed and the device is switched to data mode, there
will be a strong pull–up 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 Tempera-
ture iButton, for example. These devices need a strong
pull–up immediately after the power–consuming activity
has been initiated by a command code.
STRONG PULL–UP TO 5V, ARMED, PREDEFINED DURATION Figure 8
Figures 8 shows the timing of the strong pull–up in data
mode. At t
1–Wire bus is completed. Without any delay the
DS2480 now activates the strong pull–up and simulta-
neously starts sending the data response byte to the
host. At t
sends a pulse response byte to the host. The idle time
between t
pulse response byte, plus the response time of the host
5V
0V
2
2
1
and t
the strong pull–up ends and the DS2480
the 8th time slot of the byte sent to the
END OF 8th
TIME SLOT
3
is comprised of the time to transmit the
t
1
t
SPU
To arm the strong pull–up, 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 pull–up by gen-
erating another dummy pulse. A complete temperature
conversion sequence that shows the use of the armed
pulse is included in Section “Software Driver
Examples”.
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 pull–up must
be limited. See Table 4, parameter 011 (Strong Pull–Up
Duration) for details. Selecting infinite duration will
require a power–on or master reset cycle to get the
DS2480 back to communicating with the host.
t
2
IDLE
TIME
t
3
BEGIN OF NEXT
TIME SLOT
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DS2480