Anybody uses vintage video terminals on the Altair Due?

[Semper Talis]

Hi ,

On my journey to get more familiar with the Altair Due I tried to do what I have done in the past for fun with my old Apple II's.

I wanted to use my Apple II and Apple III as dumb terminals .

Surprisingly that did not work out that easy .

I can connect my Apple IIc to my Mac and login via serial to the Mac console to run console commands and programs on the Mac.

When I connected the Apple IIc to the Altair I ran circles around the fact that I could send commands to the Altair like DIR or LS and see the Altair would react but I could not get any signal from the Altair back into the Apple .

After  a few days of trying out all kinds of settings and rechecking that every of my vintage apple does the same I studied the Apple Super Serial Card Manual and got the right hint.

The Altair Due is using a MAX3232 chip to level shift the serial signals to RS232 levels .

But when I looked at the schematic I saw it is a pure 3 wire protocol.(TX,RX and GND)

The Apple is demanding a 5 wire connection which includes a RTS/CTS handshake.

The Altair Due does not deliver this .

The MAX3232 is able to have this as the chip has actually 4 IO lines which could be used for it , however in the Altair Due only TX and RX are connected and the RTS and CTS is just floating unconnected..

Long story short ,after realizing this I added a short on the IO Expansion board to short pin 8+7 of the 9 Pin connector . This causes a permanent ready signal to send on the handshake.

Voila , this was fixing the problem for me.

So I wonder if someone else has seen this problem when trying to connect vintage Terminals to the Altair due.I unfortunately lost my vintage DEC VT100 terminals a long time ago.

Side note for everyone who also wants to use his vintage Apple II or Apple III for this.

Everyone using a II,II+,IIe and has a super serial card installed , you can disable the handshake by switching the infamous "Jumper Block" by pointing the mysterious triangle to "Modem" instead of the usual "Terminal". This is switching the 5 wire cable connection to a 3 Wire cable connection.( I do not know this for sure but I bet they do exactly what I have done and just short the Handshake) 

If You have an Apple IIc, Apple IIc+, Apple IIgs or an Apple III this is not possible as they have pure software controlled serial cards.

All terminal software I have tried  out (I mostly use Access II and Access III) seem not to have any working software switch for it. 

They have Xon/Xoff but that is a software protocol and it seems they still need the CTS/RTS hardware handshake.

Funny enough the USB to RS323 adapters play a role too!

I have some cheap ones who seem to work fine with the 3 wire protocol ( RX,TX, GND) but doe not have the CTS and RTS connected.

My other adapter I purchased long time ago has not this problem.

So I bet he has RTS and CTS connected.( or shorted out , I have not investigated yet) 

I discovered that by using a Y serial cable and had my Mac connected to the Apple IIc in parallel to the Altair due.

I had no problem to send and receive data between the Apple IIc and the Mac but the Apple II did not receive any data send from the Altair, jet the Apple could send commands to the Altair and the response was seen on the Mac .....sounds confusing and it was having me scratching my head for some time.

Anyhow, that's for it .

In summary , short pin 8+7 on the Altair RS323 connector and simulate a hardware handshake. The problem is solved.

[Tom Lake]

I use an ADM-3A on my Due. It runs at 9600 baud and could go faster but I like the retro

feel of the slower speed. Three wires are all I need at that speed. There's no need of handshaking.

If you have a terminal that needs the other signals, use the RS-232 expansion board. That provides

all the signals you need. If you don't have the Pro Due, you'll have to buy an expander motherboard along with the RS-232

board but if you do have the Pro, then the expander board is included.

[Semper Talis]

Hi Tom,

As I said , I solved the problem for me by adding a short between pin 7+8 on the 9 pin connector of the Altair expander board ( the experimenter has this too) .

The Super serial Card on the Apple will support 50 to 19200 baud but I also prefer 9600 for all my connections.

( Except ADP wich is a disk transfer program, that goes with 115200 baud and surprisingly has no trouble with my Apple II’s and my Apple III)

In the 1990’s I had a DEC VT100 connected to my Sun Spark 1 but I never checked if there was any handshake involved.

Back then I just used this as is and did not do hardware experiments with my most precious computer :-) 

[Jeff Crilly]

All the time … back in the day (80s) when I worked with lots of RS-232 stuff.  

It was rather common to have cables that jumpered RTS/CTS.   And also DTR (so the source would “think” there’s a terminal there).

On Jul 9, 2026, at 8:08 AM, Semper Talis <sempert...@gmail.com> wrote:



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