Table des matières
Interruption 08h - System timer (Hardware Handler)
Request/Call:
no input
related memory
| address | description |
|---|---|
| 40:6C | Daily timer counter (4 bytes) |
| 40:70 | 24 hr overflow flag (1 byte) |
| 40:67 | Day counter on all products after AT |
| 40:40 | Motor shutoff counter - decremented until 0 then shuts off diskette motor |
Notes & Comments
- INT 1C is invoked as a user interrupt
- the byte at 40:70 is a flag that certain DOS functions use and adjust the date if necessary. Since this is a flag and not a counter it results in DOS (not the RTC) losing days when several midnights pass before a DOS call
- generated 18.2 times per second by the 8253 Programmable Interval Timer (PIT)
- normal INT 8 execution takes approximately 100 microseconds
see 8253