DS2438 Dallas Semiconducotr, DS2438 Datasheet - Page 24

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DS2438

Manufacturer Part Number
DS2438
Description
Smart Battery Monitor
Manufacturer
Dallas Semiconducotr
Datasheet

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SAMPLE COMMAND SEQUENCE Table 14
Example: Assuming a single DS2438 is configured for its current accumulators to function, this sequence
allows the Bus Master to read the three current accumulators.
I/O SIGNALING
The DS2438 requires strict protocols to insure data integrity. The protocol consists of several types of
signaling on one line: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these signals,
with the exception of the presence pulse, are initiated by the bus master.
The initialization sequence required to begin any communication with the DS2438 is shown in Figure 9.
A reset pulse followed by a presence pulse indicates the DS2438 is ready to send or receive data given the
correct ROM command and memory function command. The bus master transmits (Tx) a reset pulse (a
low signal for a minimum of 480 s). The bus master then releases the line and goes into a receive
mode(Rx). The 1-Wire bus is pulled to a high state via the 5 k =pull-up resistor. After detecting the
rising edge on the I/O pin, the DS2438 waits 15-60 s and then transmits the presence pulse (a low signal
for 60-240 s). DS2438 data is read and written through the use of time slots to manipulate bits and a
command word to specify the transaction.
MASTER MODE
RX
RX
RX
RX
RX
RX
RX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
DATA (LSB FIRST)
<9 data bytes>
<9 data bytes>
Presence
Presence
Presence
Presence
Presence
BEh01h
B8h01h
B8h07h
B8h07h
Reset
Reset
Reset
Reset
Reset
CCh
CCh
CCh
CCh
24 of 29
Reset pulse
Presence pulse
Skip ROM
Issue Recall Memory page 01h command
Reset pulse
Presence pulse
Skip ROM
Issue Read SP 01h command
Read scratchpad data and CRC. The ICA is
located in byte 04h
Reset pulse
Presence pulse
Skip ROM
Issue Recall Memory page 07h command
Reset pulse
Presence pulse
Skip ROM
Issue Read SP 07h command
Read scratchpad data and CRC. The CCA is
located in bytes 04h-05h and the DCA is located in
bytes 06h-07h.
Reset pulse
Presence pulse, done
COMMENTS
DS2438

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