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P87C52IFFFA Datasheet(PDF) 8 Page - NXP Semiconductors |
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P87C52IFFFA Datasheet(HTML) 8 Page - NXP Semiconductors |
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8 / 62 page  Philips Semiconductors Product specification 80C32/87C52 CMOS single-chip 8-bit microcontrollers 1996 Aug 16 8 DIFFERENCES FROM THE 80C51 Special Function Registers The special function register space is the same as the 80C51 except that the 80C32/87C52 contains the additional special function registers T2CON, RCAP2L, RCAP2H, TL2, and TH2. Since the standard 80C51 on-chip functions are identical in the 8XC52, the SFR locations, bit locations, and operation are likewise identical. The only exceptions are in the interrupt mode and interrupt priority SFRs (see Table 1). Timer/Counters In addition to timer/counters 0 and 1 of the 80C51, the 80C32/87C52 contains timer/counter 2. Like timers 0 and 1, timer 2 can operate as either an event timer or as an event counter. This is selected by bit C/T2 in the special function register T2CON (see Figure 1). It has three operating modes: capture, auto-load, and baud rate generator, which are selected by bits in the T2CON as shown in Table 2. In the Capture Mode there are two options which are selected by bit EXEN2 in T2CON. If EXEN2 = 0, then Timer 2 is a 16-bit timer or counter which upon overflowing sets bit TF2, the Timer 2 overflow bit, which can be used to generate an interrupt. If EXEN2 = 1, then Timer 2 still does the above, but with the added feature that a 1-to-0 transition at external input T2EX causes the current value in the Timer 2 registers, TL2 and TH2, to be captured into registers RCAP2L and RCAP2H, respectively. (RCAP2L and RCAP2H are new special function registers in the 80C52.) In addition, the transition at T2EX causes bit EXF2 in T2CON to be set, and EXF2 like TF2 can generate an interrupt. The Capture Mode is illustrated in Figure 2. In the auto-reload mode, there are again two options, which are selected by bit EXEN2 in T2CON. If EXEN2 = 0, then when Timer 2 rolls over it not only sets TF2 but also causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2L and RCAP2H, which are preset by software. If EXEN2 = 1, then Timer 2 still does the above, but with the added feature that a 1-to-0 transition at external input T2EX will also trigger the 16-bit reload and set EXF2. The auto-reload mode is illustrated in Figure 3. The baud rate generation mode is selected by RCLK = 1 and/or TCLK = 1. It will be described in conjunction with the serial port. Serial Port The serial port of the 8XC52 is identical to that of the 80C51 except that counter/timer 2 can be used to generate baud rates. In the 8XC52, Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON (see Figure 1). Note that the baud rate for transmit and receive can be simultaneously different. Setting RCLK and/or TCLK puts Timer into its baud rate generator mode, as shown in Figure 4. The baud rate generator mode is similar to the auto-reload mode, in that a rollover in TH2 causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and RCAP2L, which are preset by software. Now, the baud rates in Modes 1 and 3 are determined by Timer 2’s overflow rate as follows: Modes 1, 3 Baud Rate + Timer 2 Overflow Rate 16 The timer can be configured for either “timer” or “counter” operation. In the most typical applications, it is configured for “timer” operation (C/T2 = 0). “Timer” operation is a little different for Timer 2 when it’s being used as a baud rate generator. Normally, as a timer it would increment every machine cycle (thus at 1/12 the oscillator frequency). As a baud rate generator, however, it increments every state time (thus at 1/2 the oscillator frequency). In that case the baud rate is given by the formula: Modes 1, 3 Baud Rate + Oscillator Frequency 32 [65536 * (RCAP2H, RCAP2L)] where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned integer. (MSB) (LSB) Symbol Position Name and Significance TF2 T2CON.7 Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set when either RCLK or TCLK = 1. TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2 CP/RL2 EXF2 T2CON.6 Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and EXEN2 = 1. When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must be cleared by software. RCLK T2CON.5 Receive clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock in modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the receive clock. TCLK T2CON.4 Transmit clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock in modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock. EXEN2 T2CON.3 Timer 2 external enable flag. When set, allows a capture or reload to occur as a result of a negative transition on T2EX if Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX. TR2 T2CON.2 Start/stop control for Timer 2. A logic 1 starts the timer. C/T2 T2CON.1 Timer or counter select. (Timer 2) 0 = Internal timer (OSC/12) 1 = External event counter (falling edge triggered). CP/RL2 T2CON.0 Capture/Reload flag. When set, captures will occur on negative transitions at T2EX if EXEN2 = 1. When cleared, auto-reloads will occur either with Timer 2 overflows or negative transitions at T2EX when EXEN2 = 1. When either RCLK = 1 or TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2 overflow. SU00065 Figure 1. Timer/Counter 2 (T2CON) Control Register |
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