Rainbow Electronics DS2482-800 - Manual (Page 9)

DS2482-800: Eight-Channel 1-Wire Master
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Logic Level (LL)
The LL bit reports the logic state of the active 1-Wire line without initiating any 1-Wire communication. The 1-Wire
line is sampled for this purpose every time the Status Register is read. The sampling and updating of the LL bit
takes place when the host processor has addressed the DS2482 in read mode (during the acknowledge cycle),
provided that the Read Pointer is positioned at the Status Register.
Device Reset (RST)
If the RST bit is 1, the DS2482 has performed an internal reset cycle, either caused by a power-on reset or from
executing the Device Reset command. The RST bit is cleared automatically when the DS2482 executes a Write
Configuration command to restore the selection of the desired 1-Wire features.
Single Bit Result (SBR)
The SBR bit reports the logic state of the active 1-Wire line sampled at t
MSR
of a 1-Wire Single Bit command or the
first bit of a 1-Wire Triplet command. The power-on default of SBR is 0. If the 1-Wire Single Bit command sends a
0-bit, SBR should be 0. With a 1-Wire Triplet command, SBR could be 0 as well as 1, depending on the response
of the 1-Wire devices connected. The same result applies to a 1-Wire Single Bit command that sends a 1-bit.
Triplet Second Bit (TSB)
The TSB bit reports the logic state of the active 1-Wire line sampled at t
MSR
of the second bit of a 1-Wire Triplet
command. The power-on default of TSB is 0. This bit is updated only with a 1-Wire Triplet command and has no
function with other commands.
Branch Direction Taken (DIR)
Whenever a 1-Write Triplet command is executed, this bit reports to the host processor the search direction that
was chosen by the 3rd bit of the triplet. The power-on default of DIR is 0. This bit is updated only with a 1-Wire
Triplet command and has no function with other commands. For additional information see the description of the 1-
Wire Triplet command and the Dallas Application Note 187, "1-Wire Search Algorithm".
FUNCTION COMMANDS
The DS2482 understands 9 function commands, which fall into four categories: device control, I²C communication,
1-Wire setup and 1-Wire communication. The feedback path to the host is controlled by a read pointer, which is set
automatically by each function command for the host to efficiently access relevant information. The host processor
sends these commands and applicable parameters as strings of one or two bytes using the I²C interface. The I²C
protocol requires that each byte be acknowledged by the receiving party to confirm acceptance or not be
acknowledged to indicate an error condition (invalid code or parameter) or to end the communication. Details of the
I²C protocol including acknowledge are found in the I²C interface description of this document.
Device Reset
Command Code F0h
Command Parameter None
Description
Performs a global reset of device state machine logic, which in turn
selects IO0 as the active 1-Wire channel.
Terminates any ongoing 1-Wire communication.
Typical Use Device initialization after power-up; re-initialization (reset) as desired.
Restriction None (can be executed at any time)
Error Response None
Command Duration
Maximum 525ns, counted from falling SCL edge of the command code
acknowledge bit.
1-Wire Activity
Ends maximum 262.5ns after the falling SCL edge of the command code
acknowledge bit.
Read Pointer Position Status Register (for busy polling)
Status Bits Affected
RST set to 1,
1WB, PPD, SD, SBR, TSB, DIR set to 0
Configuration Bits Affected 1WS, APU, PPM, SPU set to 0