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87C52 Datasheet(PDF) 10 Page - NXP Semiconductors |
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87C52 Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 62 page  Philips Semiconductors Product specification 80C32/87C52 CMOS single-chip 8-bit microcontrollers 1996 Aug 16 10 OSC ÷ 2 C/T2 = 0 C/T2 = 1 TR2 Control TL2 (8-bits) TH2 (8-bits) ÷ 16 RCAP2L RCAP2H EXEN2 Control EXF2 Timer 2 Interrupt T2EX Pin Transition Detector T2 Pin Reload NOTE: OSC. Freq. is divided by 2, not 12. ÷ 2 “0” “1” RX Clock ÷ 16 TX Clock “0” “1” “0” “1” Timer 1 Overflow Note availability of additional external interrupt. SMOD RCLK TCLK SU00068 Figure 4. Timer 2 in Baud Rate Generator Mode Table 2. Timer 2 Operating Modes RCLK + TCLK CP/RL2 TR2 MODE 0 0 1 16-bit Auto-reload 0 1 1 16-bit Capture 1 X 1 Baud rate generator X X 0 (off) Timer 2 as a baud rate generator is shown in Figure 4. This figure is valid only if RCLK + TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2, and will not generate an interrupt. Therefore, the Timer 2 interrupt does not have to be disabled when Timer 2 is in the baud rate generator mode. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 is in use as a baud rate generator, T2EX can be used as an extra external interrupt, if desired. It should be noted that when Timer 2 is running (TR2 = 1) in “timer” function in the baud rate generator mode, one should not try to read or write TH2 or TL2. Under these conditions the timer is being incremented every state time, and the results of a read or write may not be accurate. The RCAP registers may be read, but should not be written to, because a write might overlap a reload and cause write and/or reload errors. Turn the timer off (clear TR2) before accessing the Timer 2 or RCAP registers, in this case. Timer/Counter 2 Set-up Except for the baud rate generator mode, the values given for T2CON do not include the setting of the TR2 bit. Therefore, bit TR2 must be set, separately, to turn the timer on. See Table 3 for set-up of timer 2 as a timer. See Table 4 for set-up of timer 2 as a counter. Using Timer/Counter 2 to Generate Baud Rates For this purpose, Timer 2 must be used in the baud rate generating mode. If Timer 2 is being clocked through pin T2 (P1.0) the baud rate is: Baud Rate + Timer 2 Overflow Rate 16 And if it is being clocked internally, the baud rate is: Baud Rate + Oscillator Frequency 32 [65536 * (RCAP2H, RCAP2L)] To obtain the reload value for RCAP2H and RCA02L, the above equation can be rewritten as: RCAP2H, RCAP2L + 65536 * Oscillator Frequency 32 Baud Rate |
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