Programmable dedicated timer operating on a clock independent of

Details Programmable dedicated timer operating on a clock independent of Programmable dedicated timer operating on a clock independent of

1992-06-12

1995-07-25

Kriess, Kevin A.

Boots, shoes, and leggings

3642715, 3642809, G06F 100

Patent

active

054370213

ABSTRACT:
A hardware timer dedicated to the BIOS which operates independent of the CPU timer. The BIOS activates the timer by writing a delay count to a predetermined port. Address decode circuitry identifies an address match to a write port address. When an address match coincides with a write command from the BIOS, write control circuitry coupled to the address decode circuitry activates a "load" signal for loading the delay count into a counter circuit. The counter circuit, which is coupled to the write control circuitry, operates on a clock having frequency independent of the CPU operating frequency. The counter circuit comprises a flip-flop that synchronizes the "load" signal to the clock of the counter circuit. The synchronized "load" signal causes the delay count to be loaded into the counter circuit. The write control circuitry inactivates the "load" signal such that the delay count is loaded exactly once. The counter circuit counts when the synchronized "load" signal is inactive. A count disable circuit within the counter circuit causes the counter circuit to stop counting when it reaches its terminal count.
Once counting begins, the BIOS reads from a predetermined I/O port to determine if the programmed delay has been completed through a read control circuit. The read control circuit enables a result onto the data bus of the computer system when an address match coincides with a read command from the BIOS. When the BIOS reads the terminal count, the programmed delay is complete.

REFERENCES:
patent: 4161787 (1979-07-01), Groves et al.
patent: 5247654 (1993-09-01), Hamid et al.
patent: 5274796 (1993-12-01), Conner
patent: 5297275 (1994-03-01), Thayer
Texas Instruments Manual(Preliminary) TACT84500 EISA Chip User's Guide, pp. 6-24, "EISA Peripheral Control Unit Functions", Oct. 10, 1991.

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