DS9101 datasheet(42/55 Pages) MAXIM

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Master-to-Slave

For a write-one time slot, the voltage on the data line

must have crossed the VTH threshold before the write-one

low time tW1LMAX is expired. For a write-zero time slot,

the voltage on the data line must stay below the VTH

threshold until the write-zero low time tW0LMIN is expired.

The voltage on the data line should not exceed VILMAX

during the entire tW0L or tW1L window. After the VTH

threshold has been crossed, the DS1923 needs a recov-

ery time tREC before it is ready for the next time slot.

Slave-to-Master

A read-data time slot begins like a write-one time slot.

The voltage on the data line must remain below VTL

until the read low time tRL is expired. During the tRL

window, when responding with a 0, the DS1923 starts

pulling the data line low; its internal timing generator

determines when this pulldown ends and the voltage

starts rising again. When responding with a 1, the

DS1923 does not hold the data line low at all, and the

voltage starts rising as soon as tRL is over.

The sum of tRL +

δ (rise time) on one side and the inter-

nal timing generator of the DS1923 on the other side

define the master sampling window (tMSRMIN to

tMSRMAX) in which the master must perform a read from

the data line. For most reliable communication, tRL

should be as short as permissible and the master

should read close to but no later than tMSRMAX. After

reading from the data line, the master must wait until

tSLOT is expired. This guarantees sufficient recovery

time tREC for the DS1923 to get ready for the next time

slot.

Improved Network Behavior

(Switchpoint Hysteresis)

In a 1-Wire environment, line termination is possible

only during transients controlled by the bus master (1-

Wire driver). 1-Wire networks, therefore, are susceptible

to noise of various origins. Depending on the physical

size and topology of the network, reflections from end

points and branch points can add up or cancel each

other to some extent. Such reflections are visible as

glitches or ringing on the 1-Wire communication line.

Noise coupled onto the 1-Wire line from external

sources can also result in signal glitching. A glitch dur-

ing the rising edge of a time slot can cause a slave

device to lose synchronization with the master and, as

a consequence, result in a Search ROM command

coming to a dead end or cause a device-specific func-

tion command to abort. For better performance in net-

work applications, the DS1923 uses a new 1-Wire

front-end, which makes it less sensitive to noise and

also reduces the magnitude of noise injected by the

slave device itself.

The DS1923’s 1-Wire front-end differs from traditional

slave devices in four characteristics:

1) The falling edge of the presence pulse has a con-

trolled slew rate. This provides a better match to the

line impedance than a digitally switched transistor,

converting the high-frequency ringing known from

traditional devices into a smoother, low-bandwidth

transition. The slew-rate control is specified by the

parameter tFPD, which has different values for stan-

dard and overdrive speed.

2) There is additional lowpass filtering in the circuit that

detects the falling edge at the beginning of a time

slot. This reduces the sensitivity to high-frequency

noise. This additional filtering does not apply at over-

drive speed.

3) There is a hysteresis at the low-to-high switching

threshold VTH. If a negative glitch crosses VTH but

does not go below VTH - VHY, it is not recognized

(Figure 14, Case A). The hysteresis is effective at

any 1-Wire speed.

4) There is a time window specified by the rising edge

hold-off time tREH during which glitches are ignored,

even if they extend below VTH - VHY threshold

(Figure 14, Case B, tGL < tREH). Deep voltage

droops or glitches that appear late after crossing the

VTH threshold and extend beyond the tREH window

cannot be filtered out and are taken as the begin-

ning of a new time slot (Figure 14, Case C, tGL

≥

tREH).

Devices that have the parameters tFPD, VHY, and tREH

specified in their electrical characteristics use the

improved 1-Wire front-end.

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

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