Rainbow Electronics DS2404 - Manual (Page 17)

DS2404
17 of 29
1-WIRE SIGNALING
The DS2404 requires strict protocols to ensure data integrity. The protocol consists of five types of
signaling on one line: Reset Sequence with reset pulse and presence pulse, write 0, write 1, Read Data
and interrupt pulse. All these signals except presence pulse and interrupt pulse are initiated by the bus
master.
The initialization sequence required to begin any communication with the DS2404 is shown in Figure 10.
A reset pulse followed by a presence pulse indicates the DS2404 is ready to send or receive data given the
correct ROM command and memory function command.
The bus master transmits (T
X
) a reset pulse (t
RSTL
, minimum of 480 ms). The bus master then releases the
line and goes into receive mode (R
X
). The 1-Wire bus is pulled to a high state via the pull-up resistor.
After detecting the rising edge on the date line, the DS2404 waits (t
PDH
, 15-60 ms) and then transmits the
presence pulse (t
PDL
, 60 - 240 ms). There are special conditions if interrupts are enabled where the bus
master must check the state of the 1-Wire bus after being in the R
X
mode for 480 ms. These conditions
will be discussed in the “Interrupt” section.
READ/WRITE TIME SLOTS
The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS2404 to the master
by triggering a delay circuit in the DS2404. During write time slots, the delay circuit determines when the
DS2404 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit
determines how long the DS2404 will hold the data line low overriding the 1 generated by the master. If
the data bit is a “1”, the device will leave the read data time slot unchanged.
INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 10
480 ms £ t
RSTL
< ¥ *
480 ms £ t
RSTH
< ¥ (includes recovery time)
15 ms £ t
PDH
< 60 ms
60 ms £ t
PDL
< 240 ms
* In order not to mask interrupt signaling by other devices on the 1-Wire bus, t
RSTL
+ t
R
should always
be less than 960 ms.
RESISTOR
MASTER
DS2404