How to change date and time RTC

[AlexanderSilvaB]

Hello, I'm trying to create a C function to change the time and date of the RTC, already have a function that reads data from the RTC. Please help me if you can.

Thank you.

[LindusSystem]

It is same as reading, use this code

Code: Select all

void write_cmos(unsigned char address, unsigned int value)
{
   outportb(ADDRESSREGISTER, address);
   outportb(DATAREGISTER,NMI_disable_bit << 7 | data);
}

And write to respective bits, but did u try this

[Brendan]

Hi,

Hello, I'm trying to create a C function to change the time and date of the RTC, already have a function that reads data from the RTC. Please help me if you can.

The general idea is:

• Split your time into "century, year, month, week, hour, minute, second" stored in temporary variables
• Determine if the RTC is using binary format or BCD and change everything except "hour" to suit
• Determine if the RTC is using 24 hour format or 12 hour format and change "hour" to suit (note: there's 4 cases here - 24 hour binary, 24 hour BCD, 12 hour binary, 12 hour BCD)
• Determine where the "century" goes using ACPI (the "RTC century register" field at offset 108 in the Fixed ACPI Description Table), or discard it if there's no ACPI
• Wait until the RTC's "update in progress" flag goes from "set" to "clear". There's 2 ways of doing this:
  • Polling: Loop until the flag becomes set, then loop until the flag becomes clear. This can waste up to 1 second of CPU time.
  • Use the RTC's "update IRQ" to avoid wasting CPU time. In this case the next step will be done in the IRQ handler.
• Write the values you've already prepared into the corresponding RTC/CMOS registers, in order (seconds, then minutes, then hour, then ..., then century).

Cheers,

Brendan

[AlexanderSilvaB]

Thank you...