smart idea - using an RTC chip on the Spectrum

Press RESET immediately, All! Sometimes in programs it is necessary to count time with discreteness less than 1 seconds. The RTC chip only counts in seconds. Frame interrupts (20ms period) by in any way reasons are not sufficient (for example, the modem connected via Kondratieff is working scheme with interruptions -- frame interruptions are often lost). Can be programmed A and B RTC registers for receiving periodic interrupts with a period of 31.25ms. Themselves interrupts Of course, the processor will not receive it (on the spec, the RTC interrupt output of the chip is not connected nowhere). But it is possible during each hardware interrupt (NMI, INT from the modem...) interrogate RTC status register and detect the fact of an interrupt request. If nowhere with teams DI interrupts the program does not prohibit them, they (in the case of using a modem) do not occur less often than once every 20ms (NMI or INT). In short, every 20..40ms you can receive a pulse to increase time counter at 31.25ms, regardless of modem operation. Accuracy counter depends only on the accuracy of the RTC +/- 20ms. * Originally in CODE.ZX *Crossposted in REAL.SPECCY