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PC Timer

Posted on 1998-08-11
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Last Modified: 2010-04-12
I am looking into the possibility of using PC timer for the real time measurement. I know that PC always has at least 2~3 timers. I know that Timer 2 has address of 0x42,0x43 through some articles. Can anyone tell me the address of other timers? I have been searching through all possible internet sources, yet could find the detailed descriptions.
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Question by:tangkh
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Expert Comment

by:busuka
ID: 1020547
:-???? 2-3 timers ? AFAIK, there is only one timer chip, that do
have several _channels_. One of them is PC speaker.
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LVL 12

Expert Comment

by:mark2150
ID: 1020548
The original PC design has one 8253 type timer IC mapped to I/O addresses 040-043H. There are three timer sections, T0 is used for IRQ0 time tick interrupts and provides the 18.2 ticks/second main clock. T1 is used for DMA refresh and T2 is used for the speaker control. Thus none are available for use by programs unless you can use them "as is".

There are 3rd party hardware vendors that make such things. Try:

http://www.keithley.com/Metrabyte/


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Author Comment

by:tangkh
ID: 1020549
Can you tell me the registers map and the address of this timer?
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Author Comment

by:tangkh
ID: 1020550
mark2150
I am sorry I dont mean to reject your answer. I am new to this newsgroup. When I saw "open this question to other experts", I thought I can get response from others.
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Expert Comment

by:mark2150
ID: 1020551
Ok, no problemo. That IC is not available for program use as it is fully occupied keeping your system running.

BTW the data was from the original "IBM PC Technical Reference Manual" p. D-9 (logic diagrams) and p. 1-10 I/O Address Map.

The data sheet I have handy for the 8253 is a summary. It just shows pinout and block diagram. No registers or such. I have written code to use on *external* 8253's. Each timer section has two input lines and one output. The two inputs are Clock and Gate and the output is just that, output. The timer can be set to a variety of modes of operation including one-shot, divide by N, and simple counter. Each counter is 16-bits and can count in either BDC or binary. The original part was limited to 2MHz operation but later versions clocked at higher rates.

The 8253 is currently obsolete and has been replaced by the 8254. The 8254 datasheet is available at:

http://developer.intel.com/design/periphrl/datashts/23124406.pdf

This gives you full electrical and programming specs on that device.

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Accepted Solution

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mark2150 earned 20 total points
ID: 1020552
Since I answered your question you should lock in this response so I can get the points...
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Author Comment

by:tangkh
ID: 1020553
Hahahaha, Ok you got the point, although my question wasn't really answered :)
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Author Comment

by:tangkh
ID: 1020554
On top of this, could you give me the source of the BIOS map?
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LVL 12

Expert Comment

by:mark2150
ID: 1020555
Your question *was* answered, I can't help it if the answer isn't the one you wanted! (Grin). BIOS map is from same book, "IBM PC Technical Reference". This is the granddaddy reference manual of them all. It contained not only detailed technical discussions about the features and specifications of the PC but it also included complete SCHEMATICS and the source code to the ROM BIOS! If it's incompatible with *THIS BOOK* then it ain't a PC!
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