用MC68HC705J1A对运算放大器电路的放大和衰减模拟信

This application note describes the interface between an HC705J1A and
a multiplying digital-to-analog converter (MDAC) to digitally control the
amplification or attenuation of an operational amplifier circuit. The MDAC
used is Analog Device’s DAC8043, a 12-bit, 8-pin serial device. By using
the MDAC, a mechanical potentiometer can be replaced by a more
reliable and robust solution.
The microcontroller unit (MCU) interface must be able to “talk” to the
DAC8043 using a serial communication link. The serial peripheral
interface (SPI) is one of the most widely used serial transmission
methods for communication between an MCU and a peripheral,
although not all HC05 Family members have SPI modules. An HC05
MCU without an SPI must interface with the DAC8043 using a software
input/output (I/O) driver. This method uses software bit programming to
communicate with the DAC8043. Even though it is not as efficient as the
hardware SPI method, it provides the MCU with a means to send data
to the DAC8043.