Oric V23 Modem

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Dbug
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Re: Oric V23 Modem

Post by Dbug »

So I tried otrm 380, when I'm in Prestel or Rx mode I can't do anything and I see a "-" at the bottom right, if the modem is in "Tx" mode I see a "+" at the bottom right, and I can type, but all I see are like "<ooc nooooc. (Obviously it's with the modem not connected to a proper line, I don't have the proper cable at the moment).

At least I guess it means I can now try to see if any signal pops up with the logic analyzer.

Thanks :)

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kenneth
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Re: Oric V23 Modem

Post by kenneth »

Hello

To verify the 6551 ship you can read the value of the status register (PEEK(#381) bit5) that contains the state of DCD bit, it will change when we connect pin7 of rs232Port to the ground. You can also POKE 0 in bit 3 and 0 or 1 in bit2 of the command register to change the state of RTS and verify with a multimeter. (Pin4 of the rs232Port).
You can simply connect 2 to 5 of the rs232port, what you send...will be returned. (Echo mode)
All these operations, without modem obviously.

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Re: Oric V23 Modem

Post by Dbug »

To verify the 6551 ship you can read the value of the status register (PEEK(#381) bit5) that contains the state of DCD bit, it will change when we connect pin7 of rs232Port to the ground.
So, I did a simple
10 PRINT PEEK(#381):GOTO 10
and what I have on screen is a bunch of 16, which changes to 48 when I short on the connection box the black wire (the first one in the box) with the red (2), green (3), orange (4) and copper (8), nothing happen if I connect on blue (5), white (6) or brown (7).

I guess 16 means "Transmitter empty", and 48 is the same, plus "DCD High (no carrier)".

So that means in the connection box we know one more entry
1 - Black - DCD
2 - RED - ?
3 - Green - ?
4 - Orange - GND
5 - Blue - ?
6 - White - ?
7 - Brown - ?
8 - Copper - GND

Time to get the multimeter for the rest :)

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Re: Oric V23 Modem

Post by Dbug »

By doing POKE #382,4 I get 4.22v on the green wire (3), and it gets back to 0 when I POKE #382,0, so I guess that means green is RTS.
image_2021-02-06_202801.png
Not sure if from that we can figure out a standard arrangement, definitely does not seem to match the Telestrat pinout.

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Re: Oric V23 Modem

Post by Dbug »

Ok, so with these pins that was enough to check the RS 232 port pin from the serial interface schematics.
My problem was that with DIN you are never quite sure if the pin number are done in interleaved convention or consecutive (I've seen both).

So in theory, this should be correct, and I can probably reorder the wires in the connection box so the number actually match.
image_2021-02-06_205530.png
1 - Black - DCD -> 7
2 - RED - TxD -> 2
3 - Green - RTS -> 4
4 - Orange - GND -> 3
5 - Blue - DTR -> 6
6 - White - RxD -> 5
7 - Brown - RxC -> 1
8 - Copper - GND -> Shield

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Re: Oric V23 Modem

Post by Dbug »

iss: I managed to get the connections done between the connection box and the minitel RS232 din (with the ground to the ground, rx to tx and tx to rx), and when I run your program, when I type on the Oric I do see white squares appearing on the minitel, and at the same time I see what looks like "C cedilla" on the Oric screen.

I'm not actually sure of what is supposed to happen, but at least something get sent and is received by the minitel terminal.

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Re: Oric V23 Modem

Post by kenneth »

There is something stange...The DIN connector of the rs232 is (almost) exactly the same as the Telestrat port, but the txd is connected on pin 8 on the Telestrat and pin 2 on the RS232 interface, I think that on the old schematic of the Telestrat , the number of the pin is badly writted, 2 or 8? And the pin 2 of the Telestrat is unused, maybe a mistake...

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Re: Oric V23 Modem

Post by iss »

Dbug wrote:
Sat Feb 06, 2021 9:25 pm
I'm not actually sure of what is supposed to happen, but at least something get sent and is received by the minitel terminal.
This is good! :)
Something that I forgot to suggest - try simple loopback test without the modem.
Here is some info in an old post.
Or other picture:
Image

You can start shorting only TX and RX to see if the typed characters will be echoed back, if not then do other connections.

Next, OTRM uses full 256 ASCII table HERE is the font.
And the "C cedilla" should have code 128 which is not bad number :).

At end the most important thing which I forgot too: the ACIA speed and protocol :) - this can be the explanation for the strange characters. Attached is OTRM-special-plus with TAP+DSK with base address $380 and ready to be hacked:
OTRM-hacking.png
OTRM is hard coded for 9600 baud, 8 data bits, 1 stop bit, no parity, DTR=0, RTS=1

Code: Select all

_serial_open
.(
          sei
          lda #$00
          sta _serial_stat
          sta _serial_head
          sta _serial_tail
          jmp skp1
         .byt "DBUG:CHANGE SPEED AFTER A9"
skp1
          ; 9600 baud, 8  data bits, 1 stop bit
          lda #$1e
          sta acia_ctrl

          jmp skp2
         .byt "DBUG:CHANGE PROTOCOL AFTER A9"
skp2
          ; no parity, DTR=0, RTS=1
          lda #$08
          sta acia_cmd

          inc _serial_stat
          cli
          rts
.)
You can patch #$1e and #$08 with the proper values. 6551 datasheet HERE see p.7 and p.8 - DIY software :lol:
OTRM-special-plus.zip
(39.14 KiB) Downloaded 33 times
PS : This reminds me to find some free time for an "official" release of OTRM, maybe I'll add the sources for serial port (and why not the whole program) in my open library...

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Re: Oric V23 Modem

Post by Dbug »

There is something stange...The DIN connector of the rs232 is (almost) exactly the same as the Telestrat port, but the txd is connected on pin 8 on the Telestrat and pin 2 on the RS232 interface, I think that on the old schematic of the Telestrat , the number of the pin is badly writted, 2 or 8? And the pin 2 of the Telestrat is unused, maybe a mistake...
Who knows :)
OTRM is hard coded for 9600 baud, 8 data bits, 1 stop bit, no parity, DTR=0, RTS=1
That explains it: The minitel requires 1200 bauds, 7 bits words, even parity, and one bit stop.
Probably explains why the poor thing is not able to display something valid :)
You can patch #$1e and #$08 with the proper values. 6551 datasheet HERE see p.7 and p.8 - DIY software
Ok, I'll try that, thanks.

Which brings a question: Would it make sense to have a "datasheet" category in the new Oric library, with for example proper datasheets for:
- VIA 6522
- ACIA 6551
- AY-8912 Sound chip
- WD 1793 FDC
- WD 1773 FDC
It's not technically "books", but we have developer manuals, books on electronic stuff, so why not adding the proper reference datasheets while we are at it.
And I guess the Oric service manuals would make sense as well.
PS : This reminds me to find some free time for an "official" release of OTRM, maybe I'll add the sources for serial port (and why not the whole program) in my open library...
And yeah, a simple module to just configure, send and read data over the RS232 would be nice

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Re: Oric V23 Modem

Post by Dbug »

iss wrote:
Sun Feb 07, 2021 12:58 am
You can start shorting only TX and RX to see if the typed characters will be echoed back, if not then do other connections.
That actually worked fine, there was a bit of garbage at the beginning, and then I saw what I was typing.
You can patch #$1e and #$08 with the proper values. 6551 datasheet HERE see p.7 and p.8 - DIY software :lol:
So I replaced $1e by $38 (1200 baud, 7 data bits, 1 stop bit) and $08 by $68 (even parity, DTR=0, RTS=1), but that did not seem to change much, so possibly my cable is not good, or I need other parameters.

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Re: Oric V23 Modem

Post by Chema »

I am following this with a lot of interest, as it seems to me as detective work!

Unfortunately I cannot help. Every idea I had, was already been said or was wrong after some more thought. You've done the most sensible test by crossing the cable and creating a loopback. This means the serial interface is working and generates RS-232 signals more or less correctly. I thing some older equipment would expect higher voltages for mark and space (around 12 volt) but I doubt it is the case for the minitel or even the modem.

But to avoid further possible points of failure, I would connect the cable to a PC (using a usb-rs232 converter if needed) and check with a usual terminal program. Something that dumps what arrives from the serial port and is able to send characters to it (I am sure it can be done from the command prompt, at least in a Linux system).

I find it a bit strange that you receive a 128 value from the minitel... wouldn't that be a 7-bit 0 (NULL ASCII code) plus a parity value of 1 meaning odd parity, instead of even?

Of course an oscilloscope would be great to catch what is going through the cable.

In any case I am enjoying this a lot!

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Re: Oric V23 Modem

Post by ibisum »

Was just reading OUM issues and discovered on page 9 of issue 059 there is a very detailed article on the Oric serial port:

https://library.defence-force.org/index ... &year=1992

Maybe its of some use as a reference?

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Re: Oric V23 Modem

Post by Dbug »

ibisum wrote:
Sun Feb 07, 2021 5:50 pm
Was just reading OUM issues and discovered on page 9 of issue 059 there is a very detailed article on the Oric serial port:

https://library.defence-force.org/index ... &year=1992

Maybe its of some use as a reference?
I believe I already mentioned it on the Twitter thread :)

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Re: Oric V23 Modem

Post by ibisum »

Meh, who reads twitter .. ;P

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Re: Oric V23 Modem

Post by Dbug »

Basically I do the questioning/question/testing here, but I put the summary of all the known/validated information on Twitter, so other people can learn more about the machine. And later on, I will use that as the base material for when I do the video (assuming I can get something interesting to show)

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