Talk:Jiffy Clock

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Incorrect statements[edit source]

Depending on main power input frequency[edit source]

The KERNAL uses different CIA timer values depending on the television standard the system is built for ($FDDD). A Jiffy is always 1/60th seconds long!
In contrast: The real time clock (TOD) on the CIA is derived from the main power frequency and the source frequency (50/60 Hz) must be selected properly to get correct time values for the TOD.
--JohannKlasek (talk) 22:05, 24 January 2022 (CET)

Jiffy by-one error[edit source]

The reason is that the C64 ISR does not use ADC, but instead uses SBC each jiffy when the jiffy clock is updated (TI$ and TI)[1].

This is not true. This posting quotes the correct statement, that there is no impact from the decimal mode during the timer handling in IRQ context. There is no value (proven by real code), that a 24-bit subtraction wouldn't give a wrong result (at least) in the given range. The roll-over value is recognised no matter if decimal mode is active or not. --JohannKlasek (talk) 22:05, 24 January 2022 (CET)

References[edit source]

  1. BCD math on 6502 (ADC/SBC algorithms)? accessed 24 September 2014