The circuit consists of ICM7208 seven-decade counter U1, ICM7207 oscillator controller U2, and CA3130 BIFET op amp U3. IC U1 counts input signals, decodes them to 7-segment format, and outputs signals that are used to drive a 7-digit display. IC U2 provides the timing for U1, while U3 conditions the input to U1. The 5.24288-MHz crystal frequency is divided by U2 to produce a 1280-MHz multiplexing signal at pin 12 of U2. That signal is input to pin 16 and used to scan the display digits in sequence.