This article take the classics 80C51 monolithic integrated circuit as the example, the use active status and the condition migration new concept, the new viewpoint and the new method, promulgates some monolithic integrated circuit operation the inherent laws, has certain inspiration function and the practical significance regarding the monolithic integrated circuit learner and using the exploiter.
1 monolithic integrated circuit’s active status and condition migration
80C5l monolithic integrated circuit’s each kind of activity, may describe Cheng Duoge the different active status or the working pattern. Here uses a monolithic integrated circuit active status migration chart which the author forms in one’s mind (e.g. chart l to show) explained. However, what here key attention is the reset state.
After careful analysis, may see from chart l:
①All survival condition which experiences the monolithic integrated circuit induces and describes 5 condition - - 1 shut-down condition (i.e. radio condition) and 4 active statuses.
②Only the reset state is a transition condition, other are the stable states; And each time the monolithic integrated circuit enters time the normal operation condition, must experience a reset state.
③Only then in the normal operation condition (here records makes NORMAL), the monolithic integrated circuit only then defers to the user program which in the program memory assimilates to carry out gradually along a prescribed path, thus completes each task which the exploiter designs.
④The stopped state (either the PD pattern) and the readiness for action (or the IDL pattern), is mainly the electricity saving condition which falls for the energy conservation consumes plans (or calls “sleep condition”).
⑤The only condition which leaves from the radio condition is on the electricity, what and can arrive is only a transition condition - - reset state.
⑥Outside reset state’s 4 conditions have migrate to the reset state way, is only causes the migration the condition to be different.
⑦Outside the radio condition’s 4 active status, possible to cause the monolithic integrated circuit because of momentarily the power failure to enter “the radio condition”.
⑧Migrates from other 3 active status to the reset state, basic is depends upon on exterior pin RST the reset signal. The primitive replacement source is quite single
First, this is because the traditional 80C5l replacement logic is relatively simple. If wants to increase “the power source undervoltage replacement” and “the watch-dog replacement” and so on other replacement source, then needs outside the piece to expand the independent circuit to realize.
⑨Standard 80C51 has not designed “the software to reposition” the function, if needs this function, may realize voluntarily through the user program. What is different, the software repositions cannot experience CPU a reset state.
2 replacement sources, replacement operation and reset state
Looks like in digital circuit’s sequential logic electric circuit component to need to have the reset function to be the same, each type’s monolithic integrated circuit also needs to have reset function (RESET). The reset function according to its English original intention is the reset meaning, also from the beginning starts the executive routine, or again from the beginning executive routine (Restart) meaning. The replacement is a monolithic integrated circuit’s important operation content, its goal is guaranteed that the monolithic integrated circuit movement process has a good beginning, guaranteed that in the monolithic integrated circuit movement process has a good condition.
What needs to stress: About “the replacement” a word, it both contains the replacement activity the meaning, and contains the reset state the meaning. Or, the replacement is not only a dynamic concept (refers to replacement activity, replacement operation, replacement processing or replacement process and so on), is also a static concept (refers to reset state or replacement pattern and so on).
2.1 conventional replacement source and expansion replacement source
Looking from nowadays’s technology, the standard 80C5l monolithic integrated circuit’s reset function designs the insufficient consummation highly, not only does not have the establishment to reposition the flag bit register, moreover the replacement source’s type are also very few.
So-called “replacement source”, is causes or causes the monolithic integrated circuit interior replacement fountainhead. Type quite complete monolithic integrated circuit which appears regarding the current market, its model replacement source may induce approximately into the following 6 kinds: On the electricity replacement, the artificial replacement, the power source undervoltage replacement, the watch-dog replacement, the illegal address replacement and the software reposition. These replacement source’s characteristic is:
①On the electricity repositions this kind of replacement source is essential. Because each time adds time the electricity to the monolithic integrated circuit, its supply voltage’s stability, as well as the clock oscillator’s starting of oscillation and the oscillation amplitude are stable, requires certain delay time.
②Only then on the electricity replacement and repositions these two kind of replacement source artificially, explains in the 80C51 monolithic integrated circuit’s textbook, the technical paper and the literature material is quite common.
③Regarding the power source undervoltage replacement, the watch-dog replacement and the illegal address reposition 3 kind of replacement sources, standard 80C5l do not have, but may the extra expansion, be possible through to attach some softwares or hardware’s method by the monolithic integrated circuit user according to the actual need realizes.
④Although the power source undervoltage replacement, the watch-dog replacement, the illegal address reposition 3 kind of replacement sources to be possible the extra expansion, but must draw support in replacement pin RST implements the replacement operation or replacement locking.
⑤Standard 80C51 does not have the software reset function originally, but may through the pure software way as well as the hypothesized method, realizes or the part realizes other monolithic integrated circuit’s software replacement. This method expands the software replacement is one kind of quite special replacement source; first, does not realize the replacement through the RST pin; second, the replacement operation’s content is out of the ordinary. The software repositions takes one kind of new technology, at present had more and more new monolithic integrated circuits to provide this function. For example Phililps Corporation’s P87LPC700 and the P89LPC900 series, TI-BB Corporation’s MSC1200 series, SunPlus Corporation’s SPMC65 series and so on, the interior designed has used in the control register which or the control position specially realized the software to reposition.
2.2 replacement operation actual content
The monolithic integrated circuit reset function realizes the process materially is carries on a series of replacement operation in the monolithic integrated circuit interior. In replacement period, actually did the monolithic integrated circuit internal replacement operate has completed which contents, is question which the programmers should clarify, because after the monolithic integrated circuit repositioned the operation completed the internal behavior, was the movement user program and carries on software processing the background, the foundation and the beginning.
To the 80C51 monolithic integrated circuit, only then the software repositions the actual content and the area of influence, are may have custom-made freely by the user; But every direct action on the replacement pin RST replacement source (for example on electricity replacement and so on), realizes the replacement operation’s actual content and the area of influence should be the same. Now induces as follows:
①Program counter PC returns with arrives at initial state 0000H;
②All special function register SFR returns to original state completely for the replacement value (may consult technical manual);
③All general parallel ports (PO, Pl, P2 and P3) the pin is established completely as the input state;
④Eliminates all levels of interrupt priority the activation trigger, with the aim of accepting all levels of interrupt request (only to establish 2 interrupt first ranks in standard 80C5l, but has established 4 ranks in somewhat new compatible product).
2.3 reset state concrete manifestation
Once the monolithic integrated circuit enters the reset state, and pauses under the reset state (i.e. external connection pin RST is locked in effective high level), will display the following some concrete characteristics:
◇CPU no longer the executive routine maintains static (freeze) the condition;
◇ each kind of internal periphery module (timer, serial port, bus interface, interruption system and so on) stop the work;
◇ each and the mouth (P0~P3) all mouth line outward presents the high-resistance condition;
◇ each SFR content restores to the replacement value (i.e. returns to knowing the circumstances of the matter scope);
◇ the internal RAM content maintains remembered, so long as the supply voltage is not lower than the lowest sustaining voltage (is generally 2 V) can maintain the original content;
◇ the internal clock source oscillator will still maintain the vibration, so long as the supply voltage (even slightly were also lower than in lV 1 V), the oscillator could maintain the work;
◇ each kind of piece external circuit (for example expanded memory unit, expands the I/O port or latch and so on) should maintain the original content and the condition.
2.4 additional remarks
What is worth paying attention especially, after having experienced the replacement operation each parallel port’s condition. Because the port pin is the monolithic integrated circuit relates the outside world, most kind of pins, its reset state (i.e. initialization condition) the immediate influence exterior electric circuit, will also pose the threat to the exterior electric circuit or creates the damage. In order to avoid this kind of influence or the threat, always repositions each port pin “the input mode”. The reason is, the input mode presents the very high impedance outward, thus has prevented the overflow damage which possibly effectively occurs.
Any way or any replacement source cause the replacement operation, will not change the RAM area the user data. Even undervoltage replacement event’s occurrence, so long as supply voltage VDD has not dropped the situation which cannot maintain to the RAM content (generally take 2 V as threshold), will not lose in RAM the user data.
3 several spot recent enlightenment
Once the monolithic integrated circuit system enters the PD pattern (i.e. engine off pattern, sometimes or power failure pattern, also said that “power failure protected mode”), the system clock source will stop the work, CPU as well as all pieces carries the hardware module to withdraw from the running status together, will thus cause the power loss to reduce large scale (may arrive at μA level, even below).
The monolithic integrated circuit application project development personnel may serve two kind of purposes using the engine off pattern:①Reduces the monolithic integrated circuit application system’s overall to consume energy;②When resistance supply voltage depreciation possibly brings CPU out of control, is once discovery supply voltage depreciation, undervoltage or breakdown, then thrusts forcefully the monolithic integrated circuit the engine off pattern, in order to avoid has the procedure to be chaotic. Engine off period, even if the supply voltage reduces to 2 V, still could maintain the RAM content not to lose.
May discover through the careful analysis chart 1 that initially Intel Corporation was the 80C51 establishment engine off pattern main original intention, should be based on the above second kind of goal. The reason is, may see from Figure 1, the convention awakens the way to be possible to return directly the monolithic integrated circuit from the PD pattern to the NORMAL pattern, generally the use specific interrupt source achievement awakens the source. However to standard 80C51, the Intel Corporation design has not awakened the source using the interrupt source achievement the way, has no alternative but saying that is one kind of regret.
In order to make up this regret, some new compatible products (e.g. Atmel Corporation’s AT89S5l/52/53/8252/8253, Philips Corporation’s P89V5lRB2/RC2/RD2 as well as the P89LPC900 series and so on) increased the use to enable, and is established to use level triggering exterior interrupt source INT0 and INTl takes awakens the source, after awakening the monolithic integrated circuit could after establishing the PD=l instruction the next instruction resume the movement.
