DS2438 Dallas Semiconducotr, DS2438 Datasheet - Page 25

• Manufacturer Part Number: DS2438
• Description: Smart Battery Monitor
• Manufacturer: Dallas Semiconducotr

INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 9
Write Time Slots
A write time slot is initiated when the host pulls the data line from a high (inactive) logic level to a low
logic level. There are two types of write time slots: Write 1 time slots and Write 0 time slots. All write
time slots must be a minimum of 60 s in duration with a minimum of a 1 s recovery time between
individual write cycles.
The DS2438 samples the I/O line in a window of 15 s to 60 s after the I/O line falls. If the line is high,
a Write 1 occurs. If the line is low, a Write 0 occurs (See Figure 10).
For the host to generate a Write 1 time slot, the data line must be pulled to a logic low level and then
released, allowing the data line to pull up to a high level within 15 microseconds after the start of the
write time slot. For the host to generate a Write 0 time slot, the data line must be pulled to a logic low
level and remain low for the duration of the write time slot.
Read Time Slots
The host generates read time slots when data is to be read from the DS2438. A read time slot is initiated
when the host pulls the data line from a logic high level to logic low level. The data line must remain at a
low logic level for a minimum of 1 s; output data from the DS2438 is then valid within the next 14 s
maximum.
The host therefore must stop driving the I/O pin low in order to read its state 15 s from the start of the
read slot. (see Figure 10). By the end of the read time slot, the I/O pin will pull back high via the external
pull-up resistor. All read time slots must be a minimum of 60 s in duration with a minimum of a 1 s
recovery time between individual read slots.
RESISTOR
MASTER
DS2438
480 s
480 s
15 s
60 s
25 of 29
t
t
PDH
PDL
t
t
RSTL
RSTH
< 240 s
< 60 s
<
<
*
(includes recovery time)
DS2438