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87C749 Datasheet(PDF) 6 Page - NXP Semiconductors |
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87C749 Datasheet(HTML) 6 Page - NXP Semiconductors |
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6 / 22 page  Philips Semiconductors Preliminary specification 83C749/87C749 80C51 8-bit microcontroller family 2K/64 OTP/ROM, 5 channel 8-bit A/D, PWM, low pin count 1998 Apr 23 6 OSCILLATOR CHARACTERISTICS X1 and X2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator. To drive the device from an external clock source, X1 should be driven while X2 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. IDLE MODE The 8XC749 includes the 80C51 power-down and idle mode features. In idle mode, the CPU puts itself to sleep while all of the on-chip peripherals except the A/D and PWM stay active. The functions that continue to run while in the idle mode are Timer 0, Timer I, and the interrupts. 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. Upon powering-up the circuit, or exiting from idle mode, sufficient time must be allowed for stabilization of the internal analog reference voltages before an A/D conversion is started. Special Function Registers The special function registers (directly addressable only) contain all of the 8XC751 registers except the program counter and the four register banks. Most of the 21 special function registers are used to control the on-chip peripheral hardware. Other registers include arithmetic registers (ACC, B, PSW), stack pointer (SP) and data pointer registers (DPH, DPL). Nine of the SFRs are bit addressable. Data Pointer The data pointer (DPTR) consists of a high byte (DPH) and a low byte (DPL). In the 80C51 this register allows the access of external data memory using the MOVX instruction. Since the 83C749 does not support MOVX or external memory accesses, this register is generally used as a 16-bit offset pointer of the accumulator in a MOVC instruction. DPTR may also be manipulated as two independent 8-bit registers. POWER-DOWN MODE In the power-down mode, the oscillator is stopped and the instruction to invoke power-down is the last instruction executed. Only the contents of the on-chip RAM are preserved. A hardware reset is the only way to terminate the power-down mode. The control bits for the reduced power modes are in the special function register PCON. Table 1. External Pin Status During Idle and Power-Down Modes MODE Port 0* Port 1 Port 2 Idle Data Data Data Power-down Data Data Data * Except for PWM output (P0.4). DIFFERENCES BETWEEN THE 8XC749 AND THE 80C51 Program Memory On the 8XC749, program memory is 2048 bytes long and is not externally expandable, so the 80C51 instructions MOVX, LJMP, and LCALL are not implemented. If these instructions are executed, the appropriate number of instruction cycles will take place along with external fetches; however, no operation will take place. The LJMP may not respond to all program address bits. The only fixed locations in program memory are the addresses at which execution is taken up in response to reset and interrupts, which are as follows: Program Memory Event Address Reset 000 External INT0 003 Counter/timer 0 00B External INT1 013 Timer I 01B ADC 02B PWM 033 Memory Organization The 8XC749 manipulates operands in three memory address spaces. The first is the program memory space which contains program instructions as well as constants such as look-up tables. The program memory space contains 2k bytes in the 8XC749. The second memory space is the data memory array which has a logical address space of 128 bytes. However, only the first 64 (0 to 3FH) are implemented in the 8XC749. The third memory space is the special function register array having a 128-byte address space (80H to FFH). Only selected locations in this memory space are used (see Table 2). Note that the architecture of these memory spaces (internal program memory, internal data memory, and special function registers) is identical to the 80C51, and the 8XC749 varies only in the amount of memory physically implemented. The 8XC749 does not directly address any external data or program memory spaces. For this reason, the MOVX instructions in the 80C51 instruction set are not implemented in the 83C749, nor are the alternate I/O pin functions RD and WR. I/O Ports The I/O pins provided by the 83C749 consist of port 0, port 1, and port 3. Port 0 Port 0 is a 5-bit bidirectional I/O port and includes alternate functions on some pins of this port. Pins P0.3 and P0.4 are provided with internal pullups while the remaining pins (P0.0, P0.1, and P0.2) have open drain output structures. The alternate function for port P0.4 is PWM output. If the alternate function PWM is not being used, then this pin may be used as an I/O port. |
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