intel.
8XC51FXHARDWAREDESCRIPTION
v=
m
70 m7aRNA1.
m
mmri rxrrs
b
v=
--------
meal
XTAL1----- XIAE?------
270653-27
Figure 30. Ueing the CHMOS On-Chip Oscillator
I
8XC51FX
NC~ X7AL2
Pigure31. Driving the CHMOS Parts with an
ExtemelClockSource
15.0 CPU TIMING
The internal clock generator defiies the sequence of
states that make up a machine cycle. A machine cycle
consists of 6 states, numbered S1 through S6. Each
state time lasts for two
oscillator periods. Thus a mac-
hine
cycle takes 12oscillator periodsor 1 microsecond
if the oscillator frequency is 12MHz. Each state is then
divided into a Phase 1 and Phase 2 half.
Rise and fall times are dependenton the external load-
ing that each pin must drive. They are approximately
10 nsec, measuredbetween 0.8V and 2.OV.
Propagation delays are differentfor different pins. For
a given pin they vary with pin loading, temperature,
VCc, and manufacturing lot. If the XTAL1 wavefomr
is taken as the timing reference, propagation delays
may vary from 25 to 125 nsec.
The AC Timings section of the datasheets do not refer-
ence any timing to the XTAL1
waveform. Rather, they
relate the critical edges of control and input signals to
500
11
I
4
a
12 16
CRVS7ALFREOUENCYIn MHz
270653-23
Figure32.ESRvsFrequency
each other. The timings published in the data sheets
include the etkets of-propagation delays under the
specified test condition.
ADDITIONAL REFERENCES
The
following application notes provide supplemental
informationto this document and can be found in the
Embedded Applications handbook.
1. AP-125 “Designing Microcontroller Systems for
ElectricallyNoisy Environments”
2. AP-155
“OscillatorsforMicrocontrollers”
3.AP-252“Designingwiththe80C51BH”
4, APA$10“Enhanced serial Port on the 83C51FA”
5. AP415 “83C51FA/FB PCA Cookbook”
6. AIMl “SoftwareSerirdPort Implemented with the
PCA”
7. AP-425 “Small DC Motor Control”
8. The appropriatedata sheet.
5-43
To Next Page
Loading...
Need help?
General
