DS2480B Datasheet DS2480B | P10-P12

DS2480B

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The type of time slot b2 (write 1 or write 0) is determined by the DS2480B as follows:

b2 = r

if conflict (as chosen by the host)

= b

if no conflict (there is no alternative)

= 1 if error (there is no response)

The response the host will receive during a complete pass through a Search ROM function using the

Search Accelerator consists of 16 bytes as follows:

first byte

7 6 5 4 3 2 1 0

r’

et cetera

byte

7 6 5 4 3 2 1 0

r’

As before, the index (values from 0 to 63, “n”) designates the position of the bit in the ROM ID of a

MicroLAN compatible device. The character “d” marks the discrepancy flag in that particular bit

position. The discrepancy flag will be 1 if there is a conflict, or no response in that particular bit position,

and 0 otherwise. The character “r” marks the actually chosen path at that particular bit position. The

chosen path is identical to b2 for the particular bit position of the ROM ID.

To perform a Search ROM sequence one starts with all bits r

being 0s. In case of a bus error, all

subsequent response bits r’

are 1s until the Search Accelerator is deactivated. Thus, if r’

and d

are both

1, an error has occurred during the search procedure and the last sequence has to be repeated. Otherwise

r’

(n = 0 ... 63) is the ROM code of the device that has been found and addressed.

For the next Search ROM sequence one reuses the previous set r

(n = 0 ... 63) but sets r

to 1 with “m”

being the index number of the highest discrepancy flag (that is, 1) and sets all r

to 0 with i > m. This

process is repeated until the highest discrepancy occurs in the same bit position for two consecutive

passes.

The table below shows an example for the communication between host and DS2480B to perform one

pass through the Search ROM function using the Search Accelerator. After a device has been identified

and addressed, a memory function (not specified here) is executed and finally a reset pulse is generated.

This example assumes that the DS2480B was in Command Mode and that regular 1-Wire speed is used.

DS2480B

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Search Accelerator Usage Example

Action Sequence Host TX Host RX

Generate Reset Pulse C1 CD or ED

Set Data Mode E1 (nothing)

Search ROM command F0 (as sent)

Set Command Mode E3 (nothing)

Search Accelerator On B1 (nothing)

Set Data Mode E1 (nothing)

Send 16 bytes data (response)

Set Command Mode E3 (nothing)

Search Accelerator Off A1 (nothing)

Set Data Mode E1 (nothing)

Do Memory Function

Set Command Mode E3 (nothing)

Generate Reset Pulse C1 CD or ED

CONFIGURATION COMMANDS

The DS2480B is designed to be configurable for the varying requirements of its application. When the

device powers up and/or performs a master reset cycle, the hard-wired default configuration settings take

effect. These settings will work on a short 1-Wire bus and assume regular 1-Wire communication speed.

To change these default settings and to verify the current settings, the logic of the DS2480B supports

configuration commands. A summary of the available configuration parameters, their default settings at

regular and Overdrive speed and their applicability is shown in Table 3.

Parameters not related to the communication speed on the 1-Wire bus specify the duration of the 12V

programming pulse, the duration of the strong pullup to 5V, the threshold current of the load sensor for

“dynamic” strong pullup duration, and the baud rate on the interface that connects the DS2480B to the

host. The remaining three parameters are used to modify the 1-Wire communication waveforms if one

selects “Flexible Speed” (see Communication Commands for speed selection).

Flexible speed is implemented to improve the performance of large MicroLAN Networks. This is

accomplished by:

§ limiting the slew rate on falling edges (e. g., at the beginning of time slots, to reduce ringing),

§ extending the Write-1 low time (allows the current flow through the network to end slowly, to prevent

voltage spikes from inductive kickback),

§ delaying the time point when reading a bit from the 1-Wire bus (gives the network more time to

stabilize, to get a higher voltage margin) and

§ adding extra recovery time between Write-0 time slots (allows more energy transfer through the

network, to replenish the parasite power supply of the devices on the bus).

The latter two functions are controlled by a single parameter. Taking advantage of flexible speed requires

changing one or more of these parameters from their default values. Otherwise the waveforms will be

identical to those at regular speed.

Each configuration parameter is identified by its 3-bit parameter code and can be programmed for one of

a maximum eight different values using a 3-bit value code. A matrix of parameter codes and value codes

with the associated physical values in shown in Table 4.

DS2480B

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Table 3. CONFIGURATION PARAMETER OVERVIEW

Configurable at Default

Parameter Description Par. Code Regular Flexible Overdrive Reg./Flex. Overdrive

Pulldown Slew Rate

Control

001 √ 15V/µs 15V/µs

Programming Pulse

Duration

010 √ √ √ 512µs 512µs

Strong Pullup Duration 011 √ √ √ 524ms 524ms

Write-1 Low Time 100 √ 8µs 1µs

Data Sample Offset and

Write 0 Recovery Time

101 √

3µs

1µs

3µs

Load Sensor Threshold 110 √ √ √ 3mA 3mA

RS232 Baud Rate 111 √ √ √ 9.6kbps 9.6kbps

The numbers given for parameter 001 (Pulldown Slew Rate Control) are nominal values. They may vary

to some extent and are almost independent of the load on the 1-Wire bus. Information on how to select

the optimum value of this parameter is given in the Controlled Edges section .

Parameter 110 (Load Sensor Threshold) has been implemented in order to more efficiently support the

high current demand of the crypto iButton. The load sensor is only active if “dynamic” (value code 110)

for the Strong Pullup Duration (parameter 011) has been selected. The nominal and default value for the

load sensor threshold is 3.0mA with a tolerance band of -25% to +80%. The sensor threshold should be

left at its default value; changes should only be made to compensate for tolerances. Dynamic duration

should only be used when operating crypto iButtons and not for gang-programming 1-Wire EEPROMs or

measuring temperature with multiple temperature sensors converting simultaneously.

For the parameters 010 (Programming Pulse Duration) and 011 (Strong Pullup Duration) one may select

indefinite duration. This value, however, should only be selected if one is not going to switch the device

to Data Mode. As long as the device stays in Command Mode, any pulse function (programming or

strong pullup) that uses one of these parameters can be terminated by sending the command code F1h.

Termination is not possible if the device is in Data Mode.

Parameter 111 (RS232 Baud Rate) has two functions. It selects the baud rate and allows inversion of the

signal at the RXD pin. Using one of the value codes 100 to 111 will set the polarity at RXD to the

opposite of what is defined by the logic level at the POL pin (asymmetry bit, see Figure 1). This may

reduce the component count in some applications of the device. Note that when changing the baud rate,

the DS2480B will send the command response byte at the new data rate.

A short explanation on the use of parameters 100 (Write-1 Low Time) and 101 (Data Sample

Offset/Write-0 Recovery Time) is given in the Timing Diagrams section later in this document.

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