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fjk61011
March 28th, 2017, 05:00 AM
Hi All,

I have an IBM monitor labelled 5151001. Is this an MDA monitor? I want to connect it to two PCs via a switch. I need a DB9 cable for the second PC. Is a DB9 cable for a Null Modem suitable? Also if the monitor is an MDA would a colour video card fry it? If so what type of card do I need?

The second PC, I hazard a guess, is a 5150. There are five expansion slots, a 200W PSU and an ST-255 which seems to have died. Is it in fact a 5150? There is DOS 3.? on the hard drive.

And is the empty socket beside the 8088 CPU for a maths processor?


Thanks in advance,

Francis


EDIT: I've just seen the sticky about the 5150.

Scali
March 28th, 2017, 05:10 AM
I have an IBM monitor labelled 5151001. Is this an MDA monitor?

Yes.


I want to connect it to two PCs via a switch. I need a DB9 cable for the second PC. Is a DB9 cable for a Null Modem suitable?

Yes. DB9 and DB25 are equivalent, you can get converters between the two. The most simple nulmodem cable only needs 3 wires: transmit, receive and ground. In fact, even the ground is somewhat optional.


Also if the monitor is an MDA would a colour video card fry it?

Yes, at least, if you are talking about regular CGA.
IBM's EGA can be configured to use a 5151 (only in 640x350 graphics and text mode), and it shouldn't fry the monitor, as long as you configured it correctly.


If so what type of card do I need?

MDA, Hercules or some clone card that explicitly supports the 50 Hz vertical and 18.5 kHz horizontal scanrate of the 5151.


The second PC, I hazard a guess, is a 5150. There are five expansion slots, a 200W PSU and an ST-255 which seems to have died. Is it in fact a 5150? There is DOS 3.? on the hard drive.

5 widely spaced ISA slots (usually with black brackets) are the tell-tale sign for a 5150. The 200W PSU and ST-225 would be after-market. As would be DOS 3.3.


And is the empty socket beside the 8088 CPU for a maths processor?

Yes, for an 8087 or compatible.

fjk61011
March 28th, 2017, 05:17 AM
Yes.



Yes. DB9 and DB25 are equivalent, you can get converters between the two. The most simple nulmodem cable only needs 3 wires: transmit, receive and ground. In fact, even the ground is somewhat optional.



Yes, at least, if you are talking about regular CGA.
IBM's EGA can be configured to use a 5151 (only in 640x350 graphics and text mode), and it shouldn't fry the monitor, as long as you configured it correctly.



MDA, Hercules or some clone card that explicitly supports the 50 Hz vertical and 18.5 kHz horizontal scanrate of the 5151.



5 widely spaced ISA slots (usually with black brackets) are the tell-tale sign for a 5150. The 200W PSU and ST-225 would be after-market. As would be DOS 3.3.



Yes, for an 8087 or compatible.

OK, thanks for that.

EDIT:

Is the larger port on the card a video port out as well?

Scali
March 28th, 2017, 05:34 AM
Is the larger port on the card a video port out as well?

Are you talking about the video card? MDA and Hercules have an integrated printer port, which is a DB25 connector. DB9 for TTL monitor.

fjk61011
March 28th, 2017, 05:40 AM
Are you talking about the video card? MDA and Hercules have an integrated printer port, which is a DB25 connector. DB9 for TTL monitor.

The card which in the first pc is connected by a cable to the monitor from the db9 port. The card is about 15 cm/6". The PC is in the attic. I'll check the card.

fjk61011
March 28th, 2017, 05:57 AM
The short card is only about 4" long and looks very new with a chip soldered to the board.

OK, I have a full length Hercules card with a V 112 - B socketed chip. This in neither pc.

EDIT. With the short card in the PC with the ST-255 i get the post beep and with booting from the floppy drive I get 4055 201 and a blinking cursor.

kgober
March 28th, 2017, 10:53 AM
Do not use a null modem cable to connect an MDA monitor to anything. A straight-through 9-pin cable is ok for this (not ideal, but it should work "well enough").

-ken

fjk61011
March 28th, 2017, 01:21 PM
I've sourced a straight through cable. I haven't found a specific MDA cable anywhere.

Chuck(G)
March 28th, 2017, 01:25 PM
To bring up a pet peeve of mine, the PC never used DB9 connectors. They're all DE-9 connectors (https://en.wikipedia.org/wiki/D-subminiature).

Yes, I do realize that I'm not going to change the world's opinion, but I can insist on accuracy.

A DB-9 would be 9 pins in a "B" sized D-subminiature shell.

evildragon
March 28th, 2017, 01:47 PM
To bring up a pet peeve of mine, the PC never used DB9 connectors. They're all DE-9 connectors (https://en.wikipedia.org/wiki/D-subminiature).

Yes, I do realize that I'm not going to change the world's opinion, but I can insist on accuracy.

A DB-9 would be 9 pins in a "B" sized D-subminiature shell.
And the game port used a DA-15, not a DB-15. ;)

Scali
March 28th, 2017, 02:33 PM
Do not use a null modem cable to connect an MDA monitor to anything.

Oh right, I misunderstood. I thought he wanted to use a nulmodem to connect two PCs together, because he spoke of a 'second PC'.
Yes, cable needs to be straight through (which a nulmodem is not!), and would need at least pins 1, 2, 6, 7 8, 9 connected.

Scali
March 28th, 2017, 02:34 PM
And the game port used a DA-15, not a DB-15. ;)

Yea, DB-15 is VGA :)

roberttx
March 28th, 2017, 02:42 PM
To bring up a pet peeve of mine, the PC never used DB9 connectors. They're all DE-9 connectors (https://en.wikipedia.org/wiki/D-subminiature).

Yes, I do realize that I'm not going to change the world's opinion, but I can insist on accuracy.

A DB-9 would be 9 pins in a "B" sized D-subminiature shell.

I used to share that pet peeve and strove for accuracy. Eventually, I gave up. What's the point of being accurate if nobody can find your words, because they're all searching for DB-whatever?

Sometimes, I'll get a brief surge of enthusiasm and use both the correct terminology and the DB-whatever. Often, though, I'm ashamed to say that I don't bother.

evildragon
March 28th, 2017, 03:28 PM
Yea, DB-15 is VGA :)

Nope, that's HD-15. ;)

Chuck(G)
March 28th, 2017, 04:59 PM
Nope, that's HD-15. ;)

Also known as DE-15.

evildragon
March 28th, 2017, 05:52 PM
I always wondered if there was supposed to be a disconcernable difference between DE-15 or HD-15. I always went with HD-15 because when I go through the parts drawer at Skycraft, it's listed as HD-15 due to the 3 rows of pins.

Chuck(G)
March 28th, 2017, 09:22 PM
See VGA Connector under "nomenclature" (https://en.wikipedia.org/wiki/VGA_connector). The shell is an "E" size shell, so -15 is pretty definitive.

The "HD" thing can get to be confusing. For example, the SCSI MD50 connector is often referred to as the "HD50" and it looks nothing like the DE-15.

Scali
March 29th, 2017, 01:23 AM
The joke was that VGA is often mistakenly referred to as DB-15. Try googling for it :)
I believe the official name for VGA is DE-15HD?

fjk61011
March 29th, 2017, 03:47 AM
Oh right, I misunderstood. I thought he wanted to use a nulmodem to connect two PCs together, because he spoke of a 'second PC'.
Yes, cable needs to be straight through (which a nulmodem is not!), and would need at least pins 1, 2, 6, 7 8, 9 connected.

I want to cable two PCs to one monitor via a switch. Finding it hard to find an MDA cable. Going to try 9 pin serial cables.

Stone
March 29th, 2017, 04:25 AM
Serial cables have female connectors. You want a cable with male connectors.

fjk61011
March 29th, 2017, 04:42 AM
Serial cables have female connectors. You want a cable with male connectors.

I managed to source a Male - Female one and a gender changer. Are they much different than an MDA cable?

Chuck(G)
March 29th, 2017, 09:24 AM
Serial cables have female connectors. You want a cable with male connectors.

Only for DTE. A serial cable to connect a terminal/PC (DTE) to a modem (DCE) has both male and female connectors. This wasn't always observed in practice. There are probably more terminals with female connectors than male ones, even though this defies convention. Ideally, a terminal would have a male connector for the RS232C host feeding it and a female connector for an attached printer. Such is rarely seen, however.

evildragon
March 29th, 2017, 09:34 AM
Yea, according to the wiki page Chuck had me read, DE-15HD is the proper term. Well, it actually makes much more sense now than it did before, so I'll buy that over using HD15 which seemed odd to me honestly.

AlexC
March 29th, 2017, 01:13 PM
I want to cable two PCs to one monitor via a switch. Finding it hard to find an MDA cable. Going to try 9 pin serial cables.

It is possible. I did this with a serial extension cable (male one end, female the other) connected to an old-style KVM switch that had VGA, 9-pin serial and DIN-style keyboard ports. I expected to have to do some soldering to connect extra wires inside the switchbox at least, but in fact it worked fine with the MDA monitors connected to the 9-pin serial ports. Perhaps I was lucky with the cable, though: all nine wires were connected, whereas some only have the bare minimum connections to allow a mouse to work. Same with 25-to-9-pin adapters and gender-changers.

Chuck(G)
March 29th, 2017, 02:45 PM
You can also fabricate your own VGA-to-CGA/MDA cables and use a regular VGA switch.

fjk61011
March 30th, 2017, 05:56 AM
You can also fabricate your own VGA-to-CGA/MDA cables and use a regular VGA switch.

OK, I might try that.