DS2480 Dallas Semiconducotr, DS2480 Datasheet - Page 5

• Manufacturer Part Number: DS2480
• Description: Serial 1.Wire Line Driver
• Manufacturer: Dallas Semiconducotr

After the DS2480 has reached the command mode, the
host can send commands such as 1–Wire Reset, Pulse,
Configuration, Search Accelerator and Single Bit func-
tions or switch over to the second static state called
Data Mode. In data mode the DS2480 simply converts
bytes it receives at the TXD pin into their equivalent
1–Wire wave forms and reports the results back to the
host through the RXD pin. If the Search Accelerator is
on, each byte seen at TXD will generate a 12–bit
sequence on the 1–Wire bus (see section Search
Accelerator for details). If the Strong Pull–up to 5V is
enabled (see Pulse command) each byte on the 1–Wire
bus will be followed by a pause of predefined duration
where the bus is pulled to 5V via a low impedance tran-
sistor in the 1–Wire driver circuit.
While being in the Data Mode the DS2480 checks each
byte received from the host for the reserved code that is
used to switch back to Command Mode. To be able to
write any possible code (including the reserved one) to
the 1–Wire bus, the transition to the Command Mode is
as follows: After having received the code for switching
to Command Mode, the device temporarily enters the
Check Mode where it waits for the next byte. If both
bytes are the same, the byte is sent once to the 1–Wire
bus and the device returns to the Data Mode. If the
second byte is different from the reserved code, it will be
executed as command and the device finally enters the
Command Mode. As a consequence, if the reserved
code that normally switches to Command Mode is to be
written to the 1–Wire bus, this code byte must be sent
twice (duplicated). This detail must be considered care-
fully when developing software drivers for the DS2480.
After having completed a memory function with a device
on the 1–Wire bus it is recommended to issue a Reset
Pulse. This means that the DS2480 has to be switched
to Command mode. The host then sends the appropri-
ate command code and continues performing other
tasks. If during this time a device arrives at the 1–Wire
bus it will generate a presence pulse. The DS2480 will
recognize this unsolicited presence pulse and notify the
host by sending a byte such as XXXXXX01b. The Xs
represent undefined bit values. The fact that the host
receives the byte unsolicited together with the pattern
01b in the least significant two bits marks the bus arrival.
If the DS2480 is left in Data Mode after completing a
memory function command it will not report any bus
arrival to the host.
COMMAND CODE OVERVIEW
The DS2480 is controlled by a variety of commands. All
command codes are 8 bits long. The most significant bit
of each command code distinguishes between commu-
nication and configuration commands. Configuration
commands access the configuration registers. They
can write or read any of the configurable parameters.
Communication commands use data of the configura-
tion register in order to generate activity on the 1–Wire
bus and/or (dis)arm the strong pull–up after every byte
or (de)activate the Search Accelerator without generat-
ing activity on the 1–Wire bus. Details on the command
codes are included in the State Transition diagram
(Figure 2). A full explanation is given in the subsequent
sections Communication Commands and Configura-
tion Commands.
In addition to the command codes explained in the sub-
sequent sections the DS2480 understands the follow-
ing reserved command codes:
Except for these reserved commands, the Search
Accelerator control and the first byte after power–on
reset or master reset cycle, every legal command byte
generates a response byte. The pulse termination code
triggers the response byte of the terminated pulse com-
mand. Illegal command bytes do not generate a com-
mand response byte.
Once the device is switched back from Data Mode to
Command Mode one must not repeat the E3h com-
mand while the Command Mode is still active.
COMMUNICATION COMMANDS
The DS2480 supports four communication function
commands: Reset, Single Bit, Pulse, and Search Accel-
erator control. Details on the assignment of each bit of
the command codes are shown in Table 1. The corre-
sponding command response bytes are detailed in
Table 2. The Reset, Search Accelerator Control and
Single Bit commands include bits to select the 1–Wire
communication speed (regular, flexible regular, Over-
drive). Even if a command does not generate activity on
the 1–Wire bus, these bits are latched inside the device
and will take effect immediately.
E1h
E3h
F1h
switch to Data Mode
switch to Command Mode
pulse termination
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DS2480