Handshaking on Serial Port 3

General discussions related to the Altair 8800 Clone

Handshaking on Serial Port 3

Postby mail@gabrielegan.com » October 28th, 2014, 4:05 pm

As I understand it, Serial Port 3 (the optional Audio Cassette Interface) doesn't support hardware handshaking via RTS/CTS. That being the case, how does a device like a high-speed paper tape punch/reader (shown in the latest video) connected to Serial Port 3 manage to tell the Altair when it has a byte to send (from its reader) or is ready to receive a byte (to punch)? Is it just that the Altair is always keeping ahead of the tape punch/reader so it never needs the device to pause? Presumably in the video demo of a high-speed tape punch/reader the baud rate on Serial Port 3 was set much higher than 300 baud, since the point of the demo is to show how much faster than cassette the fast paper tape is.

Sorry if these are naive questions. All I really need to know is what settings to use on the Serial Port 3 to work with a GNT-4604; the rest of the above is just me trying to make sense of what's going on!

Gabriel Egan
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Re: Handshaking on Serial Port 3

Postby AltairClone » October 28th, 2014, 6:30 pm

On the Altair, neither the boot process or the CLOAD/CSAVE process uses handshaking, so not having handhake lines on Port 3 won't be an issue.

The standard boot process on the Altair can easily keep up receiving data at a constant 9600 baud rate (960 cps). The paper tape reader reads at 350-450 cps, so if the reader is set to communicate at 9600 baud, the reader can run at full speed.

Similarly, the CLOAD command can keep up with a steady 9600 baud stream of data, so again, the reader can just run at full speed when doing a CLOAD.

The punch, however, is a different story. It can only run at 60-70 cps. Running at 600 baud will reduce output from a CSAVE command to just 60cps and not over-run the punch. However, the punch actually has a giant RAM buffer in it (it's newer technology than the Altair) and can receive and queue data at a full 9600 baud from the Altair and then feed it to the punch as fast as the punch can go.

Mike
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Re: Handshaking on Serial Port 3

Postby mail@gabrielegan.com » October 28th, 2014, 6:51 pm

Great, thanks Mike! I'll try the GNT-5601 punch/reader that I just got at 9600 baud tomorrow. Glad to know I'm making sense of the gory technical details in your superbly well-written user manuals.

Regards

Gabriel
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Re: Handshaking on Serial Port 3

Postby AltairClone » October 29th, 2014, 10:39 am

Did you purchase the reader from the machine shop in NY?
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Re: Handshaking on Serial Port 3

Postby mail@gabrielegan.com » November 6th, 2014, 4:31 pm

I got it from the chap you mentioned to me. Don't want to name him here as I don't know if he's okay with that. I also just bought another, a GNT-4604, for a company in the UK that refurbishes them.

Regards

Gabriel
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Re: Handshaking on Serial Port 3

Postby Caterman » November 27th, 2015, 9:39 am

Need a little info on the setup for a GNT4604.
I've just purchased a none runner. It's running now after a minor power supply repair and major open heart surgery on the main punch motor.
The metal used on the nose end of the can holding the front bearing is absolute rubbish, it's cracked and the bearing and retaining washers had completely come apart.
It's glued back in, but I'm thinking i'll have to re-manufacture a complete can end plate and bearing carrier for a permanent repair!
Current configuration:
Dip Switches
1 = OFF
2 = OFF
3 = OFF
4 = ON
5 = OFF
6 = ON
7 = ON
8 = OFF
Panel Switches
Mode = Line
Reader = Norm
Punch = Norm
Speed = Med
Serial to DCE port on rear of machine.
Baud Rate set at 300
Testing using Terraterm
The machine punches OK
Reading the tape is the problem starts and stops.
Using my standard Serial Cable I use with my DSI-2400 machine - Just 3 Wires (send/receive/gnd)
Thanks
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Re: Handshaking on Serial Port 3

Postby AltairClone » November 27th, 2015, 11:11 am

Yes, my motor mounts were dried out and no good anymore as well. Made a bunch of noise when I punched for the first time.

Your start/stop problem is due to the 300 baud setting. The reader can run more than ten times that fast. Set the baud rate for 9600. The Altair can easily keep up.

My switch settings are different, but these aren't your issue:

I have switch 3 up (8N1 vs 8N2).

I also have switch 6 up. This forces manual start/stop only so that no control character in he data stream starts or stops the reader.

Mike
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Re: Handshaking on Serial Port 3

Postby Caterman » November 27th, 2015, 12:09 pm

Thanks for info but the manual i have different info on the DIP's
SW-3 is for DC Codes not used in newer machines?
SW4 and SW5 look after word length
SW-4 SW-5
ON ON = 7 data bits (bit 8 must be stop bit)
OFF ON = 8 data bits (bit 9 must be stop bit)
ON OFF = 8 bits reader can transmit random data
OFF OFF = 8 bits reader will detect wrong parity and stop
SW-6 and SW-7 is for Baud Rate
for low medium and High
Ranging from 110 to 4800
My machine is a GNT4604 - KDVK12121
Rubber ant-vibration mounts are fair game to perish but for the whole of the front motor metal part to be crumbling arghh!!!
I haven't connected to altair yet that will be my next step.
What is the fastest reliable punch baud for these machines?
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Re: Handshaking on Serial Port 3

Postby Caterman » November 27th, 2015, 4:12 pm

Update - connecting to Altair to GNT4604
DIP settings changed to
1-Off, 2-Off, 3-Off, 4-Off, 5-On, 6-Off, 7-On, 8-On
Loading/Reading only unto 4800 GNT set to high speed - Possibly length of cable/ switch box?
Saving/Punching only at 300 - GNT set to medium speed
Seems a work up changing baud rate on ACR all the time?
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Re: Handshaking on Serial Port 3

Postby AltairClone » November 27th, 2015, 7:00 pm

Mine is a 4606 vs 4604, that's why the differences.

The punches used are either 50cps (300 baud ok, 600 baud too fast) or 75cps (600 baud ok). The 4606 has a huge RAM buffer, so I can dump to it at 9600 and it feeds the punch as fast as it can from the buffer.

Not sure why reads aren't working at 9600. Let me know what you find.

Mike
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