Introduction to the design method of PIC microcontroller low power consumption system-EEWORLD

Collect

③Interrupt request circuit. In order to extend the battery working time, the CPU is in a power-saving dormant state when in standby mode. When the remote telephone and local machine control the controller function, the CPU is awakened by the interrupt request circuit.

(2) Voice circuit

The voice circuit is shown in Figure 5. It takes the ISD4000 voice chip as its core, mainly stores the alarm voice, and transmits the output to the telephone line after power amplification.

(3) Interface circuit between MT8880 and PIC microcontroller

MT8880 is a DTMF transceiver from Mitel. It has the advantages of powerful functions, low power consumption, stable operation and reliability, so it has been widely used in DTMF signal modulation occasions. The interface circuit between MT8880 and PIC microcontroller is shown in Figure 6.

①Interface circuit between MT8880 and MCU. D0~D3 are 4 data lines. MT8880 demodulates the pre-processed DTMF signal, stores the demodulated signal in the on-chip register, and sends an interrupt signal to the MCU through IRQ. After the MCU responds to the interrupt request, it reads the demodulated data through D0~D3 under the control of R, W, RS0, and RD.

②DTMF signal amplification circuit. When the microprocessor writes the DTMF data to be sent into the corresponding register of MT8880, MT8880 sends out the DTMF signal from the TONE pin. After the signal is amplified by the amplifier circuit, it is sent to the transformer for voltage change.

3 Programming

When the program is running: ① is the electrical controller. If the remote phone operates the controller, it is judged according to the number of ringing tones of the phone; if the local phone operates the controller, it is judged according to the off-hook situation of the local phone. ② is the alarm. The alarm probe detects the alarm at any time and sends a signal to the controller. The controller determines whether to pull out the alarm phone according to the user's settings, whether it is in alert or not. Figure 7 is the program flow chart.

The following mainly introduces the initialization procedure, MT8880 setting subroutine and DTMF signal sending and receiving subroutine.

; Initialize registers

F0 EQU 0H

RTCCEQU 01H

PC EQU 02H

STATUS EQU 03H

FSR EQU 04H

RA EQU 05H

RB EQU 06H

RC EQU 07H

RD EQU 08H

RE EQU 09H