DS2480B+ Maxim Integrated Products, DS2480B+ Datasheet - Page 9

• Manufacturer Part Number: DS2480B+
• Description: IC LINE DRVR W/SENSOR 1-W 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Line Driver, Transmitterr

Specifications of DS2480B+

• Number Of Drivers/receivers: 1/0
• Protocol: RS232
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

During the execution of the Search ROM function, the Search Accelerator receives from the host
information on the preferred path to choose as one contiguous chain of bytes and then translates it into the
appropriate time slots on the 1-Wire bus. In addition, the Search Accelerator reports back to the host the
ROM ID of the device actually addressed and the bit positions in which conflicts were found. (If the
ROM ID of one device has a 0 in a bit position where another device has a 1, this is called a “conflict” on
the electrical level and “discrepancy” on the logical level. See Application Note 187 for a more detailed
discussion of the Search ROM.) This helps the host to select the preferred path for the next Search ROM
activity.
Since the ROM ID of all 1-Wire/iButton devices is 64 bits long and a conflict may occur in any of these
bits, the total length of data reported to the host is 128 bits or 16 bytes. To avoid data overrun (if the CPU
sends data faster than it can be processed) the protocol for the Search Accelerator operation was defined
so that one has to send as many bytes as one will receive. This way the CPU sends 16 bytes for each path
and the UART guarantees the correct data timing and frees the CPU for other tasks while the DS2480B
performs a Search ROM function.
SEARCH ACCELERATOR OPERATION
After the Search Accelerator is activated and the Data Mode is selected, the host must send 16 bytes to
complete a single Search ROM pass on the 1-Wire bus. These bytes are constructed as follows:
first byte
et cetera
16
In this scheme, the index (values from 0 to 63, “n”) designates the position of the bit in the ROM ID of a
1-Wire/iButton device. The character “x” marks bits that act as filler and do not require a specific value
(“don’t care” bits). The character “r” marks the path to go at that particular bit in case of a conflict during
the execution of the ROM Search.
For each bit position n (values from 0 to 63) the DS2480B will generate three time slots on the 1-Wire
bus. These are referenced as:
b0
b1
b2
7
r
7
r
3
63
th
byte
for the first time slot (Read Data)
for the second time slot (Read Data) and
for the third time slot (Write Data).
6
x
6
x
3
63
5
r
5
r
2
62
4
x
4
x
2
62
3
r
3
r
1
61
2
x
2
x
1
61
1
r
1
r
0
60
9 of 32
0
x
0
x
0
60