DS2480B Datasheet DS2480B | P13-P15

DS2480B

13 of 31

Table 4. CONFIGURATION PARAMETER VALUE CODES

Value Codes

Parameter Code 000 001 010 011 100 101 110 111 Unit

001 (PDSRC) 15 2.2 1.65 1.37 1.1 0.83 0.7 0.55 V/µs

010 (PPD) 32 64 128 256 512 1024 2048

µs

011 (SPUD) 16.4 65.5 131 262 524 1048 “dyn.”

100 (W1LT) 8 9 10 11 12 13 14 15 µs

101 (DSO/W0RT) 3 4 5 6 7 8 9 10 µs

110 (LOAD) 1.8 2.1 2.4 2.7 3.0 3.3 3.6 3.9 mA

111 (RBR) 9.6 19.2 57.6 115.2 9.6 19.2 57.6 115.2 kbps

The syntax of configuration commands is very simple. Each 8-bit code word contains a 3-bit parameter

code to specify the parameter and the 3-bit value code to be selected. Bit 7 of the command code is set to

0 and bit 0 is always a 1. To read the value code of a parameter, one writes all 0s for the parameter code

and puts the parameter code in place of the parameter value code. Table 5 shows the details.

The configuration command response byte is similar to the command byte itself. Bit 0 of the response

byte is always 0. When writing a parameter, the upper 7 bits are the echo of the command code. When

reading a parameter, the current value code is returned in bit positions 1 to 3 with the upper 4 bits being

the same as sent (see Table 6).

Table 5. CONFIGURATION COMMAND CODES

FUNCTION BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

Write Parameter 0 parameter code parameter value code 1

Read Parameter 0 0 0 0 parameter code 1

Table 6. CONFIGURATION COMMAND RESPONSE BYTE

FUNCTION BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

Write Parameter 0 same as sent same as sent 0

Read Parameter 0 same as sent parameter value code 0

DS2480B

14 of 31

CONTROLLED EDGES

One of the tasks of the DS2480B is to actively shape the edges of the 1-Wire communication waveforms.

This speeds up the recharging of the 1-Wire bus (rising edges) and reduces ringing of long lines (falling

edges). The circuitry for shaping rising edges is always on. The slew rate of falling edges is actively

controlled only at flexible speed and requires the parameter for slew rate control being different from its

power-on default value.

All Rising Edges

The active pullup of the rising edges reduces the rise time on the 1-Wire bus significantly compared to a

simple resistive pullup. Figure 4 shows how the DS2480B is involved in shaping a rising edge.

Figure 4. ACTIVE PULLUP

The circuit operates as follows: At t

the pulldown (induced by the DS2480B or a device on the bus) ends.

From this point on the 1-Wire bus is pulled high by the weak pullup current I

WEAKPU

provided by the

DS2480B. The slope is determined by the load on the bus and the value of the pullup current. At t

the

voltage crosses the threshold voltage V

IAPO

. Now the DS2480B switches over from the weak pullup

current I

WEAKPU

to the higher current I

ACTPU

. As a consequence, the voltage on the bus now rises faster. As

the voltage on the bus crosses the threshold V

IAPTO

at t

, a timer is started. As long as this timer is on

APUOT

), the I

ACTPU

current will continue to flow. After the timer is expired, the DS2480B will switch

back to the weak pullup current. Excessive noise on the 1-Wire line at the V

IAPTO

level can cause an

undesirable trip of the active pullup. External R-C filtering as discussed in the HARDWARE

APPLICATION EXAMPLES section and Application Note 148 should be used to prevent false triggering.

DS2480B

15 of 31

Falling Edges (DS2480B-initiated)

Whenever the DS2480B begins pulling the 1-Wire bus low to initiate a time slot, for example, it first

turns off the weak pullup current I

WEAKPU

. Then, at regular and Overdrive speeds it will generate a falling

edge at a slew rate of typically 15V/ms. This value is acceptable for short 1-Wire busses and adequate for

communication at Overdrive speed. For MicroLAN networks of more than roughly 30m length one

should always use flexible speed. One of the parameters that is adjustable at flexible speed is the slew rate

of DS2480B-initiated falling edges. The effect of the slew rate control is shown in Figure 5.

Figure 5. SLEW RATE CONTROL

As extensive tests have shown, MicroLAN networks at a length of up to 300m will perform best if the fall

time t

is in the range of 4 ± 0.5ms. This translates into a slew rate of approximately 1V/ms. This slew rate

is typically achieved by setting the configuration parameter 001 (Pulldown Slew Rate Control) to a value

of 100 (see Table 4). If the actual measured fall time is longer than the target value, one should use a

value code of 011 or lower. If the fall time is shorter, one should use a value code of 101 or higher.

Once determined, the value code for the Pulldown Slew Rate Control parameter should be stored in the

host and always be loaded into the DS2480B after a power-on or master reset cycle.

TIMING DIAGRAMS

This section explains the waveforms generated by the DS2480B on the 1-Wire bus in detail. First the

communication waveforms such as the Reset/Presence Detect Sequence and the time slots are discussed.

After that follows a detailed description of the pulse function under various conditions. The waveforms as

generated by the DS2480B may deviate slightly from specifications found in the Book of DS19xx i

Button

Standards or in data sheets of 1-Wire slave devices. However, at a closer look one will find that all of the

timing requirements are met.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P31

DS2480B

Mfr. #:

Buy DS2480B

Manufacturer:

Maxim Integrated

Description:

Buffers & Line Drivers

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet

DS2480B