Real-time clock (RTC). Compatible with esxDOS and mass storage modules: devSD, devMMC, devIDE, Just NANO SD. It allows programming and reading time using BASIC. The card comes with an esxDOS driver: RTC.SYS – enabling correct time to be saved when writing files to disk.
Time measurement is handled by the specialized DS1307 clock chip. It stores the current time (year, month, day, hour, minute, and second) and updates it every 1 second. A 32768 Hz quartz resonator is responsible for precise timekeeping.
During normal operation, the DS1307 chip is powered by the ZX Spectrum computer. When power is off, it switches to CR2032 battery power and enters sleep mode, where it only keeps time, drawing very little current (approx. 300 nA).
The Atmega32 microcontroller (MCU), clocked by an 8 MHz quartz crystal, facilitates communication between the 19-wire MUMIO communication bus and the 2-wire I2C bus of the DS1307 chip. Its task is also to simplify the DS1307 chip’s communication protocol into easy-to-use ZX BASIC commands: IN and OUT.
