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P87C528EBBB Datasheet(PDF) 11 Page - NXP Semiconductors |
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P87C528EBBB Datasheet(HTML) 11 Page - NXP Semiconductors |
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11 / 26 page  Philips Semiconductors Product specification 80C528/83C528 CMOS single-chip 8-bit microcontrollers 1995 Feb 02 11 OSCILLATOR CHARACTERISTICS XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier. The pins can be configured for use as an on-chip oscillator, as shown in the Logic Symbol. To drive the device from an external clock source, XTAL1 should be driven while XTAL2 is left unconnected. There are no requirements on the duty cycle of the external clock signal, because the input to the internal clock circuitry is through a divide-by-two flip-flop. However, minimum and maximum high and low times specified in the data sheet must be observed. RESET A reset is accomplished by holding the RST pin high for at least two machine cycles (24 oscillator periods), while the oscillator is running. To insure a good power-up reset, the RST pin must be high long enough to allow the oscillator time to start up (normally a few milliseconds) plus two machine cycles. At power-up, the voltage on VDD and RST must come up at the same time for a proper start-up. IDLE MODE In idle mode, the CPU puts itself to sleep while all of the on-chip peripherals stay active. The instruction to invoke the idle mode is the last instruction executed in the normal operating mode before the idle mode is activated. The CPU contents, the on-chip RAM, and all of the special function registers remain intact during this mode. The idle mode can be terminated either by any enabled interrupt (at which time the process is picked up at the interrupt service routine and continued), or by a hardware reset which starts the processor in the same manner as a power-on reset. POWER-DOWN MODE In the power-down mode, the oscillator is stopped and the instruction to invoke power-down is the last instruction executed. The power-down mode can be terminated by a RESET in the same way as in the 80C51 or in addition by one of two external interrupts, INT0 or INT1. A termination with an external interrupt does not affect the internal data memory and does not affect the special function registers. This makes it possible to exit power-down without changing the port output levels. To terminate the power-down mode with an external interrupt INT0 or INT1 must be switched to level-sensitive and must be enabled. The external interrupt input signal INT0 and INT1 must be kept low until the oscillator has restarted and stabilized. An instruction following the instruction that puts the device in the power-down mode will be executed. A reset generated by the watchdog timer terminates the power-down mode in the same way as an external RESET, and only the contents of the on-chip RAM are preserved. The control bits for the reduced power modes are in the special function register PCON. DESIGN CONSIDERATIONS At power-on, the voltage on VDD and RST must come up at the same time for a proper start-up. When the idle mode is terminated by a hardware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write when idle is terminated by reset, the instruction following the one that invokes idle should not be one that writes to a port pin or to external memory. Table 5 shows the state of I/O ports during low current operating modes. Table 5. External Pin Status During Idle and Power-Down Modes MODE PROGRAM MEMORY ALE PSEN PORT 0 PORT 1 PORT 2 PORT 3 Idle Internal 1 1 Data Data Data Data Idle External 1 1 Float Data Address Data Power-down Internal 0 0 Data Data Data Data Power-down External 0 0 Float Data Data Data |
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