μC makes effective frequency counter

摘要

Figure i shows an efficient and cost-effective frequency counter using an Atmel 89C2051 μC (Reference 1). The design can use any μC of the 8051 family. The circuit counts frequency and sends the count to a PC via the serial port. The signal connects to pin 3.4 of the μC. The TTL-compatible output of the μC drives the 1488, which converts the output to RS-232 voltage levels. The output of the 1488 connects to the RxD pin on the serial port of the PC. In this design, only unidirectional communication exists between the μC and the PC. But you can use the TxD line to control another device. The assembly routine in Listing 1 shows initialization of the timer, counter, and interrupts. The main program sets up T0 to count external pulses and T1 to count time in the autoreload mode 2 (Reference 2). The main program monitors the main-program flag, frqflg, until the flag is set.