DS2460ST Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated
Номер в каталоге
Компоненты Описание
производитель
DS2460ST Datasheet PDF : 8 Pages
| |||
Abridged Data Sheet
DS2460
Read and Write
This section discusses the read and write behavior of the various registers and the EEPROM. Please refer to the
full data sheet for details.
SHA-1 Engine Control
This section describes the user’s view of the SHA-1 engine and how to operate it. For details refer to the full data
sheet (includes Figures 7 to 9 and Tables 1 and 2).
SHA-1 COMPUTATION ALGORITHM
This description of the SHA computation is adapted from the Secure Hash Standard SHA-1 document that can be
downloaded from the NIST website (www.itl.nist.gov/fipspubs/fip180-1.htm). Further details are found in the full
version of the data sheet.
Application Information
SDA and SCL Pullup Resistors
SDA is an open-drain output on the DS2460 that requires a pullup resistor (Figure 10) to realize high logic levels.
Because the DS2460 uses SCL only as input (no clock stretching) the master can drive SCL either through an
open-drain/collector output with a pullup resistor or a push-pull output.
Figure 10. Application Schematic
VCC
RP
RP
VCC
SDA
SCL
µC
GND
VCC
SDA AD0
SCL
AD1
AD2
GND
To additional
2-wire devices
Example
slave
address =
100 0101
Pullup Resistor RP Sizing
According to the I²C specification, a slave device must be able to sink at least 3mA at a VOL of 0.4V. This DC
condition determines the minimum value of the pullup resistor: RPMIN = (VCC - 0.4V)/3mA. With an operating voltage
of 5.5V, the minimum value for the pullup resistor is 1.7kΩ. The "Minimum RP" line in Figure 11 shows how the
minimum pullup resistor changes with the operating (pull-up) voltage.
For I²C systems, the rise time and fall time are measured from 30% to 70% of the pullup voltage. The maximum
bus capacitance CB is 400pF. The maximum rise time must not exceed 300ns. Assuming maximum rise time, the
maximum resistor value at any given capacitance CB is calculated as: RPMAX = 300ns/(CB*ln(7/3)). For a bus
capacitance of 400pF the maximum pullup resistor would be 885Ω.
7 of 8
Share Link: 