The Contest Computer (Video Card, COM4, etc) by the 1/2 Wit

W3MM at W3MM at
Thu Dec 14 17:15:02 EST 1995

Hello J.P.  After re-reading my post I realize that I should have said
that if your video card uses the com4 address, then you will not have
com4 available for serial port use.  I can see how I may have caused 
some confusion.  I have been down the road with ATI Mach32 and 
Mach64 video cards and these cards do use the com4 address.  If
you put a serial card in the computer and have the card set for com4
and any IRQ of your choice,  then the computer locks up on the boot
and the screen turns into a checker board. 

I received a message from KB9IYS before I did this post and he was 
in desparate need of com4 but he had figured out that the video card
had somehow snatched com4 but he did not know why. He is using
a Diamond Viper SE card.

A couple of other fellows acknowledged that they also had this problem
but did not know why it was happening.  They did not indicate the brand
or model of their cards. 

I also received recommendations on various serial port cards, hard disk
controller cards with 16550 UARTS, etc.

I made an interesting observation today. I have a P5-90 and a P5-100
both of which are Gateway computers with an Intel motherboard. Both
of them use the ATI Mach64 video card. I looked at the CMOS setup
on each computer and found that each had one thing in common: com4
is locked out by the BIOS!  The selections for the on board serial ports
are com1, com2, com3, or disable. COM4 is just not there. Well now 
I knew I had to run a test.

I took a 4 port serial card and set it to com4   irq11. I put the card into
the P5-100 and then booted the computer. The computer booted with
no problem. I then ran MSD and told it to tell me about the comports.
MSD recognized the third port and said it was com3 and was using the
com3 address!  I then loaded a CT TSR and had it set for com4, irq11,
b1200, etc. It loaded fine. I then ran MSD again and got the same info 
with the exception of the baud rate. It had changed from 2400 to 1200
for the added com port. I then ran FINDIRQ. It said com4 was on irq11.
I unloaded the tsr and re-booted the confuser. I ran MSD again and the
baud rate on com3 had reverted to 2400.

It appears that the BIOS translates a request for com4 to com3 and the
com3 address.  Just some more ice on the steps.  I think Gateway 
had the BIOS writers do this because their tech support guys were 
getting swamped with calls from people trying to use com4 on these 
computers and were getting unexplainable lockups.  

I have a new P5-133 and I looked at the cmos setup on it and com4 is
available in the cmos setup, but the video card is a MATROX. Again this
                    is a Gateway computer. 

OK J.P., I hope I have clarified what I intended to share with the guys
that is there can be a potential problem with com4 and the video card.
I would guess that there is a 50-50 chance of this happening on newer
computers. I am going to share this response with reflector since it 
contains information that is relative to the next Contest Computer 
subject which is "Cereal Ports".

VY 73 de Dave  W3MM  w3mm at


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