Rainbow Electronics DS2788 - Manual (Page 28)

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8 1-Wire Signaling
The 1-Wire bus requires strict signaling protocols to
ensure data integrity. The four protocols used by the
DS2788 are as follows: the initialization sequence (reset
pulse followed by presence pulse), write-0, write-1, and
read data. All these types of signaling except the pres-
ence pulse are initiated by the bus master.
Figure 22 shows the initialization sequence required to
begin any communication with the DS2788. A presence
pulse following a reset pulse indicates that the DS2788
is ready to accept a net address command. The bus
master transmits (Tx) a reset pulse for t RSTL . The bus
master then releases the line and goes into receive
mode (Rx). The 1-Wire bus line is then pulled high by
the pullup resistor. After detecting the rising edge on
the DQ pin, the DS2788 waits for t
PDH
and then trans-
mits the presence pulse for t
PDL
.
Write-Time Slots
A write-time slot is initiated when the bus master pulls
the 1-Wire bus from a logic-high (inactive) level to a
logic-low level. There are two types of write-time slots:
write-1 and write-0. All write-time slots must be t SLOT in
duration with a 1µs minimum recovery time, t REC ,
between cycles. The DS2788 samples the 1-Wire bus
line between 15µs and 60µs (between 2µs and 6µs for
overdrive speed) after the line falls. If the line is high
when sampled, a write-1 occurs. If the line is low when
sampled, a write-0 occurs (see Figure 23). For the bus
master to generate a write-1 time slot, the bus line must
be pulled low and then released, allowing the line to be
pulled high within 15µs (2µs for overdrive speed) after
the start of the write-time slot. For the host to generate a
write-0 time slot, the bus line must be pulled low and
held low for the duration of the write-time slot.
Read-Time Slots
A read-time slot is initiated when the bus master pulls
the 1-Wire bus line from a logic-high level to a logic-low
level. The bus master must keep the bus line low for at
least 1µs and then release it to allow the DS2788 to
present valid data. The bus master can then sample
the data t RDV from the start of the read-time slot. By the
end of the read-time slot, the DS2788 releases the bus
line and allows it to be pulled high by the external
pullup resistor. All read-time slots must be t
SLOT
in
duration with a 1µs minimum recovery time, t
REC
,
between cycles. See Figure 23 for more information.
Stand-Alone Fuel-Gauge IC with
LED Display Drivers
28 ______________________________________________________________________________________
RESISTOR PULLUP
BUS MASTER ACTIVE LOW
LINE TYPE LEGEND:
DQ
DS2788 ACTIVE LOW
PK+
PK-
t RSTL t RSTH
t PDL t PDH
Figure 22. 1-Wire Initialization Sequence