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 during the rising edge of a time
slot can cause a slave device to lose synchronization with
the master and, consequently, result in a Search ROM
command coming to a dead end or cause a device-spe-
cific function command to abort. For better performance
in network applications, the DS28E36 uses a 1-Wire front-
end that is less sensitive to noise.
The DS28E36’s 1-Wire front-end has the following features:
● The falling edge of the presence pulse has a con-
trolled slew rate to reduce ringing. The slew rate con-
trol is specified by t
FPD
.
● There is a hysteresis at the low-to-high switching
threshold V
TH
. If a negative glitch crosses V
TH
, but
does not go below V
TH
- V
HY
, it is not recognized
(Figure 8, Case A). The hysteresis is effective at any
1-Wire speed.
● There is a time window specified by the rising edge
hold-off time t
REH
during which glitches are ignored,
even if they extend below the V
TH
- V
HY
threshold
(Figure 8, Case B, t
GL
< t
REH
). Deep voltage drops
or glitches that appear late after crossing the V
TH
threshold and extend beyond the t
REH
window can-
not be filtered out and are taken as the beginning of
a new time slot (Figure 8, Case C, t
GL
≥ t
REH
).
Figure 8. Noise Suppression Scheme
V
PUP
V
TH
t
REH
t
GL
t
REH
t
GL
0V
CASE A CASE B CASE C
V
HY
DS28E36 DeepCover Secure Authenticator
www.maximintegrated.com
Maxim Integrated
│
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