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P80C32 数据表(PDF) 24 Page - NXP Semiconductors |
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P80C32 数据表(HTML) 24 Page - NXP Semiconductors |
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24 / 62 page ![]() Philips Semiconductors Product data P80C3xX2; P80C5xX2; P87C5xX2 80C51 8-bit microcontroller family 4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V), low power, high speed (30/33 MHz) 2003 Jan 24 24 SM2 Enables the multiprocessor communication feature in Modes 2 and 3. In Mode 2 or 3, if SM2 is set to 1, then Rl will not be activated if the received 9th data bit (RB8) is 0. In Mode 1, if SM2=1 then RI will not be activated if a valid stop bit was not received. In Mode 0, SM2 should be 0. REN Enables serial reception. Set by software to enable reception. Clear by software to disable reception. TB8 The 9th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as desired. RB8 In Modes 2 and 3, is the 9th data bit that was received. In Mode 1, it SM2=0, RB8 is the stop bit that was received. In Mode 0, RB8 is not used. TI Transmit interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or at the beginning of the stop bit in the other modes, in any serial transmission. Must be cleared by software. RI Receive interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or halfway through the stop bit time in the other modes, in any serial reception (except see SM2). Must be cleared by software. SM0 SM1 SM2 REN TB8 RB8 TI RI Where SM0, SM1 specify the serial port mode, as follows: SM0 SM1 Mode Description Baud Rate 0 0 0 shift register fOSC/12 (12-clock mode) or fOSC/6 (6-clock mode) 0 1 1 8-bit UART variable 1 0 2 9-bit UART fOSC/64 or fOSC/32 (12-clock mode) or fOSC/32 or fOSC/16 (6-clock mode) 1 1 3 9-bit UART variable SU01626 Bit Addressable SCON Address = 98H Reset Value = 00H 76543 2 1 0 Figure 12. Serial Port Control (SCON) Register Baud Rate f SMOD Timer 1 Mode 12-clock mode 6-clock mode fOSC SMOD C/T Mode Reload Value Mode 0 Max 1.67 MHz 3.34 MHz 20 MHz X X X X Mode 2 Max 625 k 1250 k 20 MHz 1 X X X Mode 1, 3 Max 104.2 k 208.4 k 20 MHz 1 0 2 FFH Mode 1, 3 19.2 k 38.4 k 11.059 MHz 1 0 2 FDH 9.6 k 19.2 k 11.059 MHz 0 0 2 FDH 4.8 k 9.6 k 11.059 MHz 0 0 2 FAH 2.4 k 4.8 k 11.059 MHz 0 0 2 F4H 1.2 k 2.4 k 11.059 MHz 0 0 2 E8H 137.5 275 11.986 MHz 0 0 2 1DH 110 220 6 MHz 0 0 2 72H 110 220 12 MHz 0 0 1 FEEBH Figure 13. Timer 1 Generated Commonly Used Baud Rates More About Mode 0 Serial data enters and exits through RxD. TxD outputs the shift clock. 8 bits are transmitted/received: 8 data bits (LSB first). The baud rate is fixed a 1/12 the oscillator frequency (12-clock mode) or 1/6 the oscillator frequency (6-clock mode). Figure 14 shows a simplified functional diagram of the serial port in Mode 0, and associated timing. Transmission is initiated by any instruction that uses SBUF as a destination register. The “write to SBUF” signal at S6P2 also loads a 1 into the 9th position of the transmit shift register and tells the TX Control block to commence a transmission. The internal timing is such that one full machine cycle will elapse between “write to SBUF” and activation of SEND. SEND enables the output of the shift register to the alternate output function line of P3.0 and also enable SHIFT CLOCK to the alternate output function line of P3.1. SHIFT CLOCK is low during S3, S4, and S5 of every machine cycle, and high during S6, S1, and S2. At S6P2 of every machine cycle in which SEND is active, the contents of the transmit shift are shifted to the right one position. As data bits shift out to the right, zeros come in from the left. When the MSB of the data byte is at the output position of the shift register, then the 1 that was initially loaded into the 9th position, is just to the left of the MSB, and all positions to the left of that contain zeros. This condition flags the TX Control block to do one last shift and then deactivate SEND and set T1. Both of these actions occur at S1P1 of the 10th machine cycle after “write to SBUF.” Reception is initiated by the condition REN = 1 and R1 = 0. At S6P2 of the next machine cycle, the RX Control unit writes the bits 11111110 to the receive shift register, and in the next clock phase activates RECEIVE. RECEIVE enable SHIFT CLOCK to the alternate output function line of P3.1. SHIFT CLOCK makes transitions at S3P1 and S6P1 of every machine cycle. At S6P2 of every machine cycle in which RECEIVE is active, the contents of the receive shift register are |
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