Rainbow Electronics DS1985 User Manual
Page 25
DS1985
25 of 25
NOTES:
1. All voltages are referenced to ground.
2. V
PUP
= external pullup voltage. If V
PUP
is lower than 3.0V the first byte read (any read command)
may not reproduce the correct memory contents. Therefore, under low voltage conditions, it is
recommended to set either the most significant bit or all five most significant bits of TA2 to 1.
Internal circuitry of the chip will force these five bits back to 0 before they are shifted in the address
counter and CRC generator.
3. Input load is to ground.
4. An additional reset or communication sequence cannot begin until the reset high time has expired.
5. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is
guaranteed to be valid within 1
µ
s of this falling edge and will remain valid for 14
µ
s minimum. (15
µ
s total from falling edge on 1-Wire bus.)
6. V
IH
is a function of the external pullup resistor and V
PUP
.
7. 30 nanocoulombs per 72 time slots @ 5.0V.
8. At V
CC
=5.0V with a 5k
Ω
pullup to V
CC
and a maximum time slot of 120
µ
s.
9. Capacitance on the data pin could be 800 pF when power is first applied. If a 5k
Ω
resistor is used to
pull up the data line to V
CC
, 5
µ
s after power has been applied the parasite capacitance will not affect
normal communications.
10. Under certain low voltage conditions V
ILMAX
may have to be reduced to as much as 0.5V to always
guarantee a presence pulse.