DS2490 View Datasheet(PDF) - Dallas Semiconductor -> Maxim Integrated

Part Name

Description

Manufacturer

DS2490

USB to 1-WireTM Bridge Chip

Dallas Semiconductor -> Maxim Integrated 

WRITE 0 TIME SLOT Figure 7

DS2490

Speed

tLOW0 tREC0 tSLOT

Regular 62 µs 6 µs

68 µs

Overdrive 7 µs

3 µs

10 µs

Flexible 62 µs

3 to 10 65 to 72

µs

µs

*Power-up defaults for Flexible speed: tREC0=7µs

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

computer intervention. See the MODE COMMAND section for details on duration times. The

processing of a PULSE command is essentially the same, regardless if 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

cable must be short, 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.

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