PDF 89C55 Data sheet ( Hoja de datos )

Número de pieza	89C55
Descripción	8-Bit Microcontroller with 20K Bytes Flash
Fabricantes	ATMEL Corporation
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No Preview Available ! AT89C55 Features • Compatible with MCS-51™ Products • 20K Bytes of In-System Reprogrammable Flash Memory – Endurance: 1,000 Write/Erase Cycles • Fully Static Operation: 0 Hz to 33 MHz • Three-Level Program Memory Lock • 256 x 8-bit Internal RAM • 32 Programmable I/O Lines • Three 16-bit Timer/Counters • Eight Interrupt Sources • Low Power Idle and Power Down Modes Description The AT89C55 is a low-power, high-performance CMOS 8-bit microcomputer with 20K bytes of Flash programmable and erasable read only memory. The device is manu- factured using Atmel’s high density nonvolatile memory technology and is compatible with the industry standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C55 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. (continued) Pin Configurations PDIP 8-Bit Microcontroller with 20K Bytes Flash AT89C55 PQFP/TQFP PLCC 0580D-A–12/97 4-169 1 page AT89C55 Table 1. AT89C55 SFR Map and Reset Values 0F8H 0F0H 0E8H 0E0H 0D8H 0D0H 0C8H 0C0H 0B8H 0B0H 0A8H 0A0H 98H 90H 88H 80H B 00000000 ACC 00000000 PSW 00000000 T2CON 00000000 IP XX000000 P3 11111111 IE 0X000000 P2 11111111 SCON 00000000 P1 11111111 TCON 00000000 P0 11111111 T2MOD XXXXXX00 SBUF XXXXXXXX TMOD 00000000 SP 00000111 RCAP2L 00000000 TL0 00000000 DPL 00000000 RCAP2H 00000000 TL1 00000000 DPH 00000000 TL2 00000000 TH0 00000000 TH2 00000000 TH1 00000000 0FFH 0F7H 0EFH 0E7H 0DFH 0D7H 0CFH 0C7H 0BFH 0B7H 0AFH 0A7H 9FH 97H 8FH PCON 0XXX0000 87H 4-173 5 Page AT89C55 Programmable Clock Out A 50% duty cycle clock can be programmed to come out on P1.0, as shown in Figure 5. This pin, besides being a regu- lar I/O pin, has two alternate functions. It can be pro- grammed to input the external clock for Timer/Counter 2 or to output a 50% duty cycle clock ranging from 61 Hz to 4 MHz at a 16 MHz operating frequency. To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the timer. The clock-out frequency depends on the oscillator fre- quency and the reload value of Timer 2 capture registers (RCAP2H, TCAP2L), as shown in the following equation: Clock-Out Frequency = 4-----×-----[---6---5---5-O---5--s-3--c-6--i-l--l–-a---t-(-o-R--r--C--F---A-r--e-P--q--2-u--H--e--,-n-R--c--C-y----A----P----2---L----)---] In the clock-out mode, Timer 2 roll-overs will not generate an interrupt. This behavior is similar to when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a baud-rate generator and a clock generator simulta- neously. Note, however, that the baud-rate and clock-out frequencies cannot be determined independently from one another since they both use RCAP2H and RCAP2L. UART The UART in the AT89C55 operates the same way as the UART in the AT89C51 and AT89C52. For further informa- tion, see the Microcontroller Data Book, section titled, “Serial Interface.” Table 5. Interrupt Enable (IE) Register (MSB) (LSB) EA — ET2 ES ET1 EX1 ET0 EX0 Enable Bit = 1 enables the interrupt. Enable Bit = 0 disables the interrupt. Symbol Position Function Disables all interrupts. If EA = 0, no interrupt is acknowledged. If EA = EA IE.7 1, each interrupt source is individually enabled or disabled by setting or clearing its enable bit. — IE.6 Reserved. ET2 IE.5 Timer 2 interrupt enable bit. ES IE.4 Serial Port interrupt enable bit. ET1 IE.3 Timer 1 interrupt enable bit. EX1 IE.2 External interrupt 1 enable bit. ET0 IE.1 Timer 0 interrupt enable bit. EX0 IE.0 External interrupt 0 enable bit. User software should never write 1s to unimplemented bits, because they may be used in future AT89 products. Figure 6. Interrupt Sources Interrupts The AT89C55 has a total of six interrupt vectors: two exter- nal interrupts (INT0 and INT1), three timer interrupts (Tim- ers 0, 1, and 2), and the serial port interrupt. These inter- rupts are all shown in Figure 6. Each of these interrupt sources can be individually enabled or disabled by setting or clearing a bit in Special Function Register IE. IE also contains a global disable bit, EA, which disables all interrupts at once. Note that Table 5 shows that bit position IE.6 is unimple- mented. In the AT89C51 and AT89LV51, bit position IE.5 is also unimplemented. User software should not write 1s to these bit positions, since they may be used in future AT89 products. Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register T2CON. Neither of these flags is cleared by hardware when the service routine is vectored to. In fact, the service routine may have to determine whether it was TF2 or EXF2 that generated the interrupt, and that bit will have to be cleared in software. The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers overflow. The values are then polled by the circuitry in the next cycle. However, 4-179 11 Page

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