DS2480 Dallas Semiconducotr, DS2480 Datasheet - Page 18

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

SINGLE BIT WITH STRONG PULL–UP
Similar to the pulse command the Single Bit command
also allows generating a strong pull–up immediately fol-
lowing a time slot. The strong pull–up of the Single Bit
command, however, is controlled directly by bit 1 of the
command code and therefore needs not be armed.
Since the DS2480 remains in command mode when
using the Single Bit command, any duration of the
strong pull–up including infinite may be selected.
SINGLE BIT WITH STRONG PULL–UP, PREDEFINED DURATION Figure 9a
For predefined duration (Figure 9a) the timing is as fol-
lows: At t
activates the strong pull–up and simultaneously starts
sending the response byte of the Single Bit command to
the host. At t
sends out a pulse response byte. The idle time between
t
response byte, plus the response time of the host plus
the time to transmit the command and/or data to gener-
ate the next time slot.
SINGLE BIT WITH STRONG PULL–UP, INFINITE DURATION Figure 9b
The minimum duration of a strong pull–up of infinite
duration strongly depends on the baud rate of the com-
munication between host and DS2480. The host must
first receive the response byte of the single–bit com-
mand, react to it and then transmit the termination com-
2
DS2480
042498 18/26
and t
3
5V
0V
5V
0V
1
is comprised of the time to transmit the pulse
the time slot is completed. Now the DS2480
2
END OF PREVIOUS
the strong pull–up ends and the DS2480
END OF PREVIOUS
TIME SLOT
TIME SLOT
t
t
1
1
STRONG PULL–UP ON
t
SPU
Figure 9 shows the timing of the Single Bit command
with the immediately following strong pull–up. Strong
pull–up immediately following a single time slot is imple-
mented to support the DS1954 Crypto iButton. After
having received the command code to run a program,
the Crypto iButton sends out an acknowledge bit and
then starts the microcomputer to run the firmware pro-
gram for a predefined time.
For infinite duration (Figure 9b) the strong pull–up also
begins immediately after the time slot is completed. To
end the strong pull–up, the DS2480 must receive a ter-
mination command, code F1h, which occurs at t
termination command does not generate a response
byte. The DS2480 will then immediately end the strong
pull–up and send out a pulse response byte. Everything
else is the same as with predefined duration.
mand. Neglecting the hosts response time, the shortest
duration of an infinite strong pull–up therefore is
173.6 s at 115.2 kbps, 347.2 s at 57.6 kbps, 1.04 ms
at 19.2 kbps and 2.08 ms at 9.6 kbps.
t
t
2
2
IDLE
TIME
TIME
IDLE
t
t
3
3
BEGIN OF NEXT
BEGIN OF NEXT
ACTIVITY
ACTIVITY
2
. The