Difference between revisions of "Timer and Divider Registers"
(New page: ===FF04 - DIV - Divider Register (R/W)=== This register is incremented at rate of 16384Hz (~16779Hz on SGB). In CGB Double Speed Mode it is incremented twice as fast, ie. at 32768Hz. Writi...) |
(→INT 50 - Timer Interrupt) |
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Each time when the timer overflows (ie. when TIMA gets bigger than FFh), then an interrupt is requested by setting Bit 2 in the IF Register (FF0F). When that interrupt is enabled, then the CPU will execute it by calling the timer interrupt vector at 0050h. | Each time when the timer overflows (ie. when TIMA gets bigger than FFh), then an interrupt is requested by setting Bit 2 in the IF Register (FF0F). When that interrupt is enabled, then the CPU will execute it by calling the timer interrupt vector at 0050h. | ||
| − | + | == Note == | |
The above described Timer is the built-in timer in the gameboy. It has nothing to do with the MBC3s battery buffered Real Time Clock - that's a completely different thing, described in the chapter about Memory Banking Controllers. | The above described Timer is the built-in timer in the gameboy. It has nothing to do with the MBC3s battery buffered Real Time Clock - that's a completely different thing, described in the chapter about Memory Banking Controllers. | ||
Revision as of 05:39, 28 June 2009
Contents
FF04 - DIV - Divider Register (R/W)
This register is incremented at rate of 16384Hz (~16779Hz on SGB). In CGB Double Speed Mode it is incremented twice as fast, ie. at 32768Hz. Writing any value to this register resets it to 00h.
FF05 - TIMA - Timer counter (R/W)
This timer is incremented by a clock frequency specified by the TAC register ($FF07). When the value overflows (gets bigger than FFh) then it will be reset to the value specified in TMA (FF06), and an interrupt will be requested, as described below.
FF06 - TMA - Timer Modulo (R/W)
When the TIMA overflows, this data will be loaded.
FF07 - TAC - Timer Control (R/W)
Bit 2 - Timer Stop (0=Stop, 1=Start)
Bits 1-0 - Input Clock Select
00: 4096 Hz (~4194 Hz SGB)
01: 262144 Hz (~268400 Hz SGB)
10: 65536 Hz (~67110 Hz SGB)
11: 16384 Hz (~16780 Hz SGB)
INT 50 - Timer Interrupt
Each time when the timer overflows (ie. when TIMA gets bigger than FFh), then an interrupt is requested by setting Bit 2 in the IF Register (FF0F). When that interrupt is enabled, then the CPU will execute it by calling the timer interrupt vector at 0050h.
Note
The above described Timer is the built-in timer in the gameboy. It has nothing to do with the MBC3s battery buffered Real Time Clock - that's a completely different thing, described in the chapter about Memory Banking Controllers.
