DS1977 Maxim, DS1977 Datasheet - Page 20

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

Figure 10. INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES”
After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to V
the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold V
DS1977 waits for t
pulse, the master must test the logical state of the 1-Wire line at t
The t
DS1977 is ready for data communication. In a mixed population network t
480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-Wire devices.
READ/WRITE-TIME SLOTS
Data communication with the DS1977 takes place in time slots, which carry a single bit each. Write-time slots
transport data from bus master to slave. Read-time slots transfer data from slave to master. The definitions of the
write and read-time slots are illustrated in Figure 11.
All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the
threshold V
during a write-time slot and how long data will be valid during a read-time slot.
MASTER-TO-SLAVE
For a write-one time slot, the voltage on the data line must have crossed the V
low time t
threshold until the write-zero low time t
line should not exceed V
DS1977 needs a recovery time t
Figure 11. READ/WRITE TIMING DIAGRAM
Write-One Time Slot
RSTH
window must be at least the sum of t
W1LMAX
V
TL
IHMASTER
, the DS1977 starts its internal timing generator that determines when the data line will be sampled
V
V
ILMAX
V
V
PUP
0V
is expired. For a write-zero time slot, the voltage on the data line must stay below the V
TH
TL
PDH
t
F
and then transmits a Presence Pulse by pulling the line low for t
RESISTOR
ILMAX
during the entire t
t
REC
W1L
before it is ready for the next time slot
ε
W0LMIN
is expired. For most reliable communication the voltage on the data
PDHMAX
W0L
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window. After the V
, t
MASTER
PDLMAX
, and t
MSP
.
RECMIN
.
THMAX
. Immediately after t
RSTH
t
SLOT
THMAX
threshold has been crossed, the
should be extended to minimum
threshold after the write-one
PDL
. To detect a presence
RSTH
TH
is crossed, the
is expired, the
DS1977
PUP
THMIN
via