Newbie quesion about serial connection

66 views
Skip to first unread message

Thomas Riesen

unread,
Jun 25, 2021, 11:32:14 PM6/25/21
to SEBHC
Hi all

Thanks for letting me join the group. I recenetly acquired a H8, had to fix some problems, but now the system seems to work well.

Sorry, but I have a really "newbie" question:
I would like to connect the H8 to a serial terminal, the system contains only the standard Monitor software, so, is it possible "get in contact" with the system and work with the Monitor only with this standard Monitor software in place?

Thank you for your help!

Thomas


Tim Gilberts

unread,
Jun 26, 2021, 6:26:19 AM6/26/21
to se...@googlegroups.com
Thomas,

I am no expert as a new owner myself so others will probably correct me. PAM (the monitor) does include serial handling routines but, you need a serial card.   My machine has the H8-5 which is a cassette and serial card - there is also a four port UART card (H8-4) I think but, someone else will need to clarify if a specific level of PAM is needed to use that one.



I have my H8-5 hooked up to a terminal emulator at 9600 baud and it works well but, you have to watch the IRQ arrangements at least on my version of PAM.  This is something I am still investigating.

Tim
--
You received this message because you are subscribed to the Google Groups "SEBHC" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sebhc+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/2b2efaa5-be50-4989-951f-d815b22a4fbcn%40googlegroups.com.


glenn.f...@gmail.com

unread,
Jun 26, 2021, 6:56:27 AM6/26/21
to se...@googlegroups.com

As Tim says, the key is to have the H-8-5 serial interface card. Thomas: do you have this board on your system?  The PAM monitor load/dump routines are specifically designed to work with this board.  The later H-8-4 serial card is a wonderful board but is more useful in a disk-based setup.

 

The H-8-5 has two 8251 universal synchronous asynchronous receiver transmitter (USART) chips; one intended for interfacing to the console (typically an H9 terminal back in the early days) and one for loading software (typically a cassette drive back in the early days). I have successfully used Dave Runkle’s adapter to convert the second 8251 (cassette port) into an RS232 serial port which can be connected to a PC (see his writeup “Adding a RS232 Interface to the H8-5 Cassette Interface” at http://www.astrorat.com/heathkit/heathkith8computer.html).  I then have been able to load the various tape images (in “H8T” format) using a PC to replace the cassette drive.  There is a set of images at https://sebhc.github.io/sebhc/software/tapes/tape-images.zip.  The very early H8 documentation can be helpful with this (“Software Reference Manual” 595-2048). I have a paper copy but am not sure if/where there’s a PDF of this.

 

Now I believe it is not necessary to actually build this adapter as the original H-8-5 was also designed to work with ASR teletype machines, which were popular among early computer hobbyists. Using the “port interchange” switch on the board I believe you can use the first USART to do double duty, functioning as both a console port and a serial interface port.  This feature was intended to support paper tape punch/readers which were a common accessory in the ASR world.  I haven’t worked out the details on this but it seems like putting the switch in “PORT INTCHG” mode will let you do this.  See the H-8-5 manual at the link provided in Tim’s email, and specifically page 44.

 

 

Let us know if you are successful and/or if you need more help.  It would be good to document how to use this feature with a modern PC setup and serial connection…

 

Davie Troendle and I have also resurrected some of the very early BASIC programs from HUG volumes I-V (which were published only in printed form). I haven’t posted this anywhere, mostly since I didn’t perceive too much interest, but both Tim and Thomas, and perhaps others may be interested since it lets you load and run software without relying on ancient cassette recorders and without needing an operational H17 disk system.  If there’s interest I can provide more help/info here…

 

  • Glenn
image001.png

Tim Gilberts

unread,
Jun 26, 2021, 7:01:22 AM6/26/21
to se...@googlegroups.com
I can confirm that the Port Interchange allows the Dump and Load to be used to save and get files from the terminal - that is something I have tried and will cover in my next video.

What I have not done is worked out how to load the existing library of data that way... it sounds like those early programs will be of interest but, I will need to prove I can load Harbour BASIC that way first... it may just work I have not tried it just Dumping the memory test code and reloading it.

I am hoping to have some time over the next week to explore and document this interesting aspect of the Card.

Tim

Thomas Riesen

unread,
Jun 26, 2021, 7:29:09 AM6/26/21
to SEBHC
@all: Thank you for your help!

@Tim: What Videos do you talk about?

And sorry, forgot to attach a picture of my system, I think I have the appropriate serial board ... isn't it?

Thomas

Heathkit_H8_rt_01.jpg

Tim Gilberts

unread,
Jun 26, 2021, 7:33:36 AM6/26/21
to se...@googlegroups.com
Thomas,

Ah yes you have both boards there very nice... 5 serial ports and a tape interface (which is a serial port with analogue circuits) - the H8-5 is the one on the back so if it does not already have a cable you will need to make one.

I am running a series of YouTube videos as I restore a H8... I have just got onto the serial card - it is towards the end after the memory in Part 3...  You may wish to watch at least the first part for some background as well.


Tim

Glenn Roberts

unread,
Jun 26, 2021, 7:49:40 AM6/26/21
to se...@googlegroups.com
You have both, which is fine. For starting out you may want to just remove the H-8-4 

Sent from my iPad

On Jun 26, 2021, at 7:29 AM, Thomas Riesen <gast...@gmail.com> wrote:

@all: Thank you for your help!
To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/5457c117-ab31-486a-bf26-cb0b41a70b7fn%40googlegroups.com.
<Heathkit_H8_rt_01.jpg>

dwight

unread,
Jun 28, 2021, 11:25:37 PM6/28/21
to se...@googlegroups.com
Hi
The H8-4 can be used at 9600 but one has to tweak the bias on the optical isolator. This is a problem caused by designers looking at the manufacture specification and not realizing that they are under optimal conditions of load. The optical isolator turns on fast with a high resistance load and turns off fast with a low resistance load. To run a square wave you need to do both at the same time. I consider 4800 as the maximum rate on can expect on the H8-4.
Dwight


From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Glenn Roberts <glenn.f...@gmail.com>
Sent: Saturday, June 26, 2021 4:49 AM
To: se...@googlegroups.com <se...@googlegroups.com>

glenn.f...@gmail.com

unread,
Jun 29, 2021, 8:30:02 AM6/29/21
to se...@googlegroups.com

Just to clarify, it’s the (older, 1977) H-8-5 serial board that has the optical isolation. Heathkit clearly wasn’t thinking in terms of anything we’d call “high speed” today.  In the instructions they recommend setting the board to 110 BAUD for Teletype; 300 BAUD for the “high speed” H36 (LA36 DecWriter II); and 600 BAUD for the H9 video terminal!  I can’t remember but don’t think the H9 could even go past 4800? 😊

 

When the H19 and H-8-4 came out (1979) 9600 BAUD became standard for Heathkit (and the aftermarket soon was pushing that to 19.2K and higher).

Mark Garlanger

unread,
Jun 29, 2021, 8:26:08 PM6/29/21
to se...@googlegroups.com
Hi Dwight,

  I think you mean the H8-5, not the H8-4. The H8-5 is the one with the tape player support. The H8-4 is the standard one with up to four 8250s, and is used with the H19 at 9600 baud.

Mark


To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/BYAPR01MB531926EB0D82C3D381682530A3059%40BYAPR01MB5319.prod.exchangelabs.com.

dwight

unread,
Jun 30, 2021, 9:30:54 AM6/30/21
to se...@googlegroups.com
As usual, you are correct, Mark. It isn't a problem with the serial chip, it is the optical coupler that is used. It is there for the TTY but still in the path for RS232. Some times it will work at 9600 but not always.
It has been a long time since I delt with it and have some brain fade.
Dwight


From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Mark Garlanger <garl...@gmail.com>
Sent: Monday, June 28, 2021 8:31 PM
Reply all
Reply to author
Forward
0 new messages