MC94MX21DVKN3 Freescale, MC94MX21DVKN3 Datasheet - Page 59

• Manufacturer Part Number: MC94MX21DVKN3
• Manufacturer: Freescale

Specifications of MC94MX21DVKN3

• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

The precision of the generated clock is very important to get a proper behavior of the one-wire module.
This module is based on a state machine which undertakes actions at defined times.
The most stringent constraint is 0.0645 as a relative time imprecision.
The time relative precision is directly derived from the frequency of the derivative clock (f):
The
This shows that the user should take care of the main clock frequency when using the one-wire module. If
the main clock is an exact integer multiple of 1 MHz, then the generated frequency will be exactly 1 MHz.
Freescale Semiconductor
RSTL
PST
RSTH
LOW0
LOWR
READ_sample
Figure 38
Times
Time relative precision = 1/f -1 = divider/clock (MHz) - 1
A main clock frequency below 10 MHz might cause a misbehavior of the module.
Read Timing
one-wire
BUS
gathers relative time precision for different main clock frequencies.
Clock divide ratio
Generated frequency (MHz)
Relative time imprecision
Main Clock Frequency (MHz)
(Microsec)
Set WR1/RD
Values
511
512
100
68
13
5
5us
13us
Table 37. System Timing Requirements
Read “0” Slot 117us
Table 38. System Clock Requirements
60us
MC94MX21 Technical Data, Rev. 1.
One-Wire samples
(set RDST)
Figure 49. Read Timing
(Microsec)
Minimum
Auto Clear WR1/RD Set WR1/RD
480
480
60
60
–
1
NOTE:
13
13
1
0
(microsec)
Maximum
120
75
15
15
–
–
5us
0.9882
0.0117
13us
16.8
17
Read “1” Slot 117us
One-Wire samples
(set RDST)
Precision
Absolute
19.44
1.023
0.023
19
Auto Clear WR1/R
31
32
20
7
4
2
Specifications
Precision
Relative
0.0645
0.0645
0.15
0.1
0.2
0.8
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