DS1267B
The C
OUT
output of the DS1267B can be used to drive the DQ input of another DS1267B. When
connecting multiple devices, the total number of bits transmitted is always 17 times the number of
DS1267Bs in the daisy chain.
An optional feedback resistor can be placed between the C
OUT
terminal of the last device and the first
DS1267B DQ input, thus allowing the controlling processor to read as well as write data or circularly
clock data through the daisy chain. The value of the feedback or isolation resistor should be in the range
from 2Ω to 10kΩ.
When reading data via the C
OUT
pin and isolation resistor, the DQ line is left floating by the reading
device. When
is driven high, bit 17 is present on the C
OUT
pin, which is fed back to the input DQ
pin through the isolation resistor. When the CLK input transitions low to high, bit 17 is loaded into the
first position of the I/O shift register and bit 16 becomes present on C
OUT
and DQ of the next device. After
17 bits (or 17 times the number of DS1267Bs in the daisy chain), the data has shifted completely around
and back to its original position. When
transitions to the low state to end data transfer, the value (the
same as before the read occurred) is loaded into the wiper-0, wiper-1, and stack select bit I/O register.
ABSOLUTE AND RELATIVE LINEARITY
Absolute linearity, also known as integral nonlinearity, is defined as the difference between the actual
measured output voltage and the expected output voltage. Figure 5 presents the test circuit used to
measure absolute linearity. Absolute linearity is given in terms of a minimum increment or expected
output when the wiper is moved one position. In the case of the test circuit, a minimum increment (MI) or
one LSB would equal 10/512 volts. The equation for absolute linearity is given as follows:
(1) ABSOLUTE LINEARITY (INL)
AL={V
O
(actual) - V
O
(expected)}/MI
Relative Linearity, also known as differential nonlinearity, is a measure of error between two adjacent
wiper position points and is given in terms of MI by equation (2).
(2) RELATIVE LINEARITY (DNL)
RL={V
O
(n+1) - V
O
(n)}/MI
Figure 6 is a plot of absolute linearity and relative linearity versus wiper position for the DS1267B at
25°C. The specification for absolute linearity of the DS1267B is ±0.75 MI typical. The specification for
relative linearity of the DS1267B is ±0.3 MI typical.
Maxim Integrated ............................................................................................................................................................................................. 5
