DS1977 Maxim, DS1977 Datasheet - Page 21

• Manufacturer Part Number: DS1977
• Description: The DS1977 is a 32KB EEPROM in a rugged iButton® enclosure
• Manufacturer: Maxim

Figure 11. READ/WRITE TIMING DIAGRAM (continued)
Write-Zero Time Slot
Read-Data 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 V
the read low time t
data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again.
When responding with a 1, the DS1977 will not hold the data line low at all, and the voltage starts rising as soon as
t
The sum of t
the master sampling window (t
most reliable communication, t
than t
recovery time t
IMPROVED NETWORK BEHAVIOR
1-Wire networks can only be terminated during transients controlled by the bus master (1-Wire driver) and are
therefore 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. A glitch during 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. For better performance in network applications, the DS1977 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 1-Wire front end of the DS1977 differs from traditional slave devices in four characteristics.
1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to the line
RL
is over.
impedance than a digitally switched transistor, converting the high frequency ringing known from traditional
MSRMAX
V
. After reading from the data line, the master must wait until t
IHMASTER
RL
V
REC
V
+ δ (rise rime) on one side and the internal timing generator of the DS1977 on the other side define
ILMAX
V
V
PUP
0V
TH
TL
for the DS1977 to get ready for the next time slot.
RL
is expired. During the t
t
F
RESISTOR
RL
MSRMIN
should be as short as permissible and the master should read close to but no later
to t
t
MSRMAX
W0L
RL
window, when responding with a 0, the DS1977 will start pulling the
) in which the master must perform a read from the data line. For
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MASTER
t
SLOT
SLOT
is expired. This guarantees sufficient
ε
t
REC
TLMIN
DS1977
until