How to Memorize COM ports and I/O Addresses...

Member Posts: 1 ■□□□□□□□□□
Here's a little trick I came up with that you might find useful...

COM1 - 03F8
COM2 - 02F8
COM3 - 03E8
COM4 - 02E8

Now, to use the trick, first look and the number after 0. We'll use 02F8 in the example.

02F8

This number can tell us if the COM port will be odd or even. In this case, the first number after 0 is 2, an even number. So, the COM port will be even as well, COM2 or COM4.

In the next part we can look at is the letter after that number.

02F8

I like to think that "F" stands for first. So, if the letter if "F", it's the first in its odd or even pair, COM1 in the odd pair or COM2 in the even pair. I haven't come up with what "E" could stand for, but by elimination you know it's the second in its pair if it's not "F" for first - COM3 or COM4. In this case, the letter is "F", so we know that this I/O address is first in it's pair.

When we put this information together, we can determine that 02F8 is the first in the even pair, or COM2.

I hope you find it helpful. It seems a bit complicated at first, but once you understand it, it's invaluable.

• Member Posts: 152
The "E" stand for "Extra". I saw that example somewhere on this board or in one of the books I read about that portion of the test. That's a good way to remember it and you will definitely need to know your IRQ's, COM's, and I/O's.
"Me fail English? That's unpossible."
• Member Posts: 54 ■■□□□□□□□□
COM1 - IRQ4 03F8
COM2 - IRQ3 02F8
COM3 - IRQ4 03E8
COM4 - IRQ3 02E8

Take a close look to the matrix the second colum has something in common. 4-3-4-3 and the third one 3-2-3-2
Just learn that sequence and you will remember that, imagine the matrix
And for the letter order just remember the word " FE " FF.EE
and you will remember that the first two address are FF and Second EE

jeje greets
• Member Posts: 13 ■□□□□□□□□□
I have dumber way of rememberin this.

IRQ 0- System clock
IRQ 1- Keyboard
IRQ 2- (2 & 9 linked)
IRQ 3- It is Com2's Fate (2F to be IRQ3. It is Com4's fate to bE late (2E
IRQ 4- It is Com1's Tripple Fate (3F to be IRQ4. It is Com3's fate to bE late (3E
IRQ 5- The Liberation of Palestine Terrorists have 2 gods (LPT2) and they attacked twice in 1978. (27
IRQ 6- Floppy has six letters therefor it is IRQ 6
IRQ 7- Little Paul Trammel has one Toy (LPT1) and he was lost 3 times in 1978 (37
IRQ 8- Realtime clock has eight letters so it is IRQ8
IRQ 10- Red light district (open for business)
IRQ 11- Red light district (open for business)
IRQ 12- Mighty_MOUSE has twelve characters (including space) therefor it is IRQ12
IRQ 13- Mathco processors are evil so they go on IRQ13
IRQ 14- Primary IDE has one foe because it is primary. (1F0)
IRQ 15- Secondary IDE has 170 foes be cause it is last. (170)
• Member Posts: 32 ■■□□□□□□□□
With the IRQ's I made up some flash cards and went through them A BUNCH of times. as for the IO's here's a tip I saw here on this web site.

There are 9 addresses, they are all in 3 digit hexadecimal format. Each one ends in the number "8 or 0". But the first two hex digits vary with each address. So remember this mnemonic:

3 2 3 2 3 2 1 1 3 F F E E 7 7 F 7 F 8 8 8 8 8 8 0 0 0

Now write the 3s,2s 1s and the3 as a column:
3
2
3
2
3
2
1
1
3
And add the rest as a second column:
3F
2F
3E
2E
37
27
1F
17
3F
Now add an "8" to the first 6 & 0s to the remaining 3 end of each row.
3F8
2F8
3E8
2E8
378
278
1F0
170
3F0
That is a list of all 9 addresses. And, in order, they correspond to COM 1,2,3,4 and LPT 1 and 2, Prim IDE Second. IDE & Floppy.

3F8: COM 1
2F8: COM 2
3E8: COM 3
2E8: COM 4
378: LPT 1
278: LPT 2
1F0: Primary IDE
170: Secondary IDE
3F0: Floppy

All you need to remember "3-2-3-2-3-2-1-1-3-F-F-E-E-7-7-F-7-F-8-8
? 8-8-8-8-0-0-0
• Member Posts: 6 ■□□□□□□□□□
I really can't believe they still have this kind of stuff on the A+ exams. In the real tech world, you encounter one of these IRQ deals in a million. At that point, it's time to get a new computer, or to consult a little manual outlining the IRQ stuff. I suppose when you start dealing with SCSI you might get this? But who really needs expensive SCSI anymore? Is it really that advantageous?

-Allan Nevala