
DS2490
8 of 50
WRITE 0 TIME SLOT Figure 7
NOMINAL TIMING VALUES
SPEED
t
LOW0
t
REC0
t
SLOT
REGULAR
62s
6s
68s
OVERDRIVE
7s
3s
10s
FLEXIBLE*
62s
3s to 10s 65s to 72s
*Powerup defaults for Flexible speed: t
REC0
= 7s
Pulse Wave Forms
The PULSE COMMUNICATION COMMAND can be used to generate either a strong pullup to 5V or
12V programming pulse. The duration of the pulses are specified with the STRONG PULLUP
DURATION and PROG PULSE DURATION mode registers. Figure 8 and Figure 9 show timing of the
two pulse types. For predefined pulse durations, tSPU and tPP are known values, for semi-infinite and
infinite durations these pulse times vary and depend on the characteristics of attached 1-Wire devices
and/or host processor intervention. See the MODE COMMAND section for details on duration times.
The processing of a PULSE command is essentially the same, regardless of whether a strong pullup or a
programming pulse is specified. As shown in the figures, at t1 processing of the PULSE command begins,
at t2 the pulse ends.
For EPROM programming, only a single slave device should be connected to the 1-Wire bus and the
physical connection between the DS2490 and EPROM device should be as short as possible, not to
exceed a few meters. The slew rate of the rising and falling edge of the programming pulse (“steep
slopes”) is actively controlled by DS2490 as shown in Figure 9. Do not attempt to generate a
programming pulse with a non-EPROM device on the bus; this may damage the device as well as the
DS2490. In addition, a correct programming pulse can only be generated if the 12V programming voltage
is available at the VPP pin of the DS2490.
Certain applications may require a duration for a strong pullup or programming pulse that cannot be
realized using one of the predefined values (see MODE COMMANDS section for values). Selecting
infinite duration allows the host to generate pulses of any length. As a consequence, however, the host
becomes responsible to actively control the duration of the pulse. Failing to do so may require a power-on
reset or master-reset cycle of the DS2490. For this reason, infinite duration should only be used if
absolutely necessary. The HALT EXECUTION WHEN DONE or HALT EXECUTION WHEN IDLE
control commands are used to terminate an infinite duration pulse. As before, processing the command is
essentially the same, regardless if it is for a strong pullup or a programming pulse.