DS2480B
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The minimum duration of a strong pullup of infinite duration strongly depends on the baud rate of the
communication between host and DS2480B. The host must first receive the response byte of the Single
Bit command, react to it and then transmit the termination command. Neglecting the host’s response time,
the shortest duration of an infinite strong pullup therefore is 173.6ms at 115.2kbps, 347.2ms at 57.6kbps,
1.04ms at 19.2kbps, and 2.08ms at 9.6kbps.
SOFTWARE DRIVER EXAMPLES
The DS2480B requires a software driver that translates the activities to be generated on the 1-Wire bus
into the appropriate commands. The examples below cover typical situations, such as reading the ROM,
writing to the scratchpad of a Memory iButton, reading the memory of a Memory iButton, programming
an Add-Only iButton EPROM and performing a temperature conversion with the DS1920 temperature
iButton. An example for the use of the Search Accelerator is included in the Search Accelerator section
found earlier in this document.
The DS2480B command codes used in these examples are valid for regular speed and will work properly
on short 1-Wire buses (<10m). The response byte on the reset command assumes a normal presence
pulse, no alarm or short.
The DS2480B includes a 1-byte buffer that stores a byte received from the host while the previous byte is
being translated into activity on the 1-Wire bus. For this reason the host may send another byte even
without having received the response byte. Sending bytes faster than they can be translated into 1-Wire
activities may result in loss of data and/or synchronization and therefore should be avoided.
READ ROM SEQUENCE
Action Sequence Host TX Host RX
Generate Reset Pulse C1 CD or ED
Set Data Mode E1 (nothing)
Read ROM Command 33 (as sent)
Read ROM ID (8 bytes) FF (x8) ROM ID
Set Command Mode E3 (nothing)
Generate Reset Pulse C1 CD or ED
WRITE SCRATCHPAD SEQUENCE
Write 2 bytes to scratchpad at memory locations 16h and 17h
Action Sequence Host TX Host RX
Generate Reset Pulse C1 CD or ED
Set Data Mode E1 (nothing)
Skip ROM Command CC CC
Write Scratchpad Command 0F (as sent)
Starting Address TA1 16 (as sent)
Starting Address TA2 00 (as sent)
Write to the Scratchpad (2 bytes) (as sent)
Set Command Mode E3 (nothing)
Generate Reset Pulse C1 CD or ED
