CODEWITHSUNDEEP
assemblyx86intelx86-16
gowtham .n
gowtham .n

Reputation: 11

Frequency of 8254 Timer

I am new to assembly language. I Want to Know what is the actual frequency of timer chip 8254.

I gone through the internet and found many different answers like maximum frequency is 8 MHz, 1.1 MHz ,etc.,

 Which one is right?

Upvotes: 0

Views: 303

Answers (1)

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521569

The Wikipedia page on 8253 and 8254 timing chips seems to imply that the answser to your question is 1.1 MHz:

The timer that is used by the system on x86 PCs is Channel 0, and its clock ticks at a theoretical value of 1193181.8181... Hz, i.e. one third of the NTSC color subcarrier frequency, which comes from dividing the system clock (14.31818 MHz) by 12.

The Wikipedia page implies that the chip had a frequency which is a multiple of the NTSC color subcarrier frequency of 3.6 MHz. I can argue against 8 MHz being the timing frequency because it is not a multiple of 8 MHz (8 / 3.6 = 2.2).

Upvotes: 3

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