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87C754 Datasheet(PDF) 10 Page - NXP Semiconductors |
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87C754 Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 26 page  Philips Semiconductors Preliminary specification 83C754/87C754 80C51 8-bit microcontroller family 4K/256 OTP/ROM, DAC, comparator, UART, reference 1998 Apr 23 10 COUNTER/TIMER The 8XC754 counter/timers are designated Timer 0 and 1. They are identical to the 80C51 counter/timers. (Timer 1 shares its interrupt with the serial port.) Programmable Counter Array (PCA) The Programmable Counter Array is a special Timer that has one 16-bit capture/compare module associated with it. The module can be programmed to operate in one of four modes: rising and/or falling edge capture, software timer, high-speed output, or pulse width modulator. The basic PCA configuration is shown in Figure 5. The PCA timer can be programmed to run at: 1/12 the oscillator frequency, 1/4 the oscillator frequency, the Timer 0 overflow, or the input on the ECI pin (P3.1). The timer count source is determined from the CPS1 and CPS0 bits in the CMOD SFR as follows (see Figure 8): CPS1 CPS0 PCA Timer Count Source 0 0 1/12 oscillator frequency 0 1 1/4 oscillator frequency 1 0 Timer 0 overflow 1 1 External Input at ECI pin In the CMOD SFR are three additional bits associated with the PCA. They are CIDL which allows the PCA to stop during idle mode, WDTE which enables or disables the watchdog function, and ECF which when set causes an interrupt and the PCA overflow flag, CF (in the CCON SFR) to be set when the PCA timer overflows. These functions are shown in Figure 6. The watchdog timer function is implemented in module 4 as implemented in other parts that have a PCA that are available on the market. The CCON SFR contains the run control bit for the PCA and the flags for the PCA timer (CF) and module (refer to Figure 9). To run the PCA the CR bit (CCON.6) must be set by software. The PCA is shut off by clearing this bit. The CF bit (CCON.7) is set when the PCA counter overflows and an interrupt will be generated if the ECF bit in the CMOD register is set, The CF bit can only be cleared by software. Bit 4 of the CCON register is the flag for the module and is set by hardware when either a match or a capture occurs. This flag can only be cleared by software. The PCA interrupt system shown in Figure 7. The CCAPM register contains the bits that control the mode in which the module will operate. The ECCF bit enables the CCF flag in the CCON SFR to generate an interrupt when a match or compare occurs in the associated module. PWM (CCAPM.1) enables the pulse width modulation mode. The TOG bit (CCAPM.2) when set causes the CEX output associated with the module to toggle when there is a match between the PCA counter and the module’s capture/compare register. The match bit MAT (CCAPM.3), when set, will cause the CCF bit in the CCON register to be set when there is a match between the PCA counter and the module’s capture/compare register. The next two bits CAPN (CCAPM.4) and CAPP (CCAPM.5) determine the edge that a capture input will be active on. The CAPN bit enables the negative edge, and the CAPP bit enables the positive edge. If both bits are set both edges will be enabled and a capture will occur for either transition. The last bit in the register ECOM (CCAPM.6) when set enables the comparator function. Figure 11 shows the CCAPM settings for the various PCA functions. There are two additional registers associated with the PCA module. They are CCAPH and CCAPL and these are the registers that store the 16-bit count when a capture occurs or a compare should occur. When the module is used in the PWM mode these registers are used to control the duty cycle of the output. PCA Capture Mode To use the PCA module in the capture mode, either one or both of the CCAPM bits CAPN and CAPP must be set. The external CEX input for the module is sampled for transition. When a valid transition occurs, the PCA hardware loads the value of the PCA counter registers (CH and CL) into the module’s capture registers (CCAPL and CCAPH). If the CCF bit for the module in the CCON SFR and the ECCF bit in the CCAPM SFR are set, then an interrupt will be generated. Refer to Figure 12. 16-bit Software Timer Mode The PCA modules can be used as software timers by setting both the ECOM and MAT bits in the module’s CCAPM register. The PCA timer will be compared to the module’s capture registers and when a match occurs an interrupt will occur if the CCF (CCON SFR) and the ECCF (CCAPM SFR) bits for the module are both set (see Figure 13). High Speed Output Mode In this mode the CEX output associated with the PCA module will toggle each time a match occurs between the PCA counter and the module’s capture registers. To activate this mode the TOG, MAT, and ECOM bits in the module’s CCAPM SFR must be set (see Figure 14). Pulse Width Modulator Mode The PCA module can be used as a PWM output. Figure 15 shows the PWM function. The frequency of the output depends on the source for the PCA timer. The duty cycle of the module is independently variable using the module’s capture register CCAPL. When the value of the PCA CL SFR is less than the value in the module’s CCAPL SFR, the output will be low, when it is equal to or greater than the output will be high. When CL overflows from FF to 00, CCAPL is reloaded with the value in CCAPH. This allows updating the PWM without glitches. The PWM and ECOM bits in the module’s CCAPM register must be set to enable the PWM mode. MODULE FUNCTIONS: 16-BIT CAPTURE 16-BIT TIMER 16-BIT HIGH SPEED OUTPUT 8-BIT PWM WATCHDOG TIMER PCA MODULE P1.1/CEX 16 BITS PCA TIMER/COUNTER TIME BASE FOR PCA MODULES 16 BITS SU00672B Figure 5. Programmable Counter Array (PCA) |
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