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Thread: RCP/M, PMMI Modem, and Altair modem program

  1. Default

    Quote Originally Posted by glitch View Post
    The Grex system still supports XMODEM transfers. I know their dialins will accept calls as low as 1200 baud, but I don't have a slower modem to try with. You can dial them at (734) 484-0512 -- if the connection works, read through the information on creating a new account at . I use my account with them to transfer files from my various computers over ftp or sftp and then pull them down using Kermit or XMODEM.
    Thanks, I tried the connection and received the following message from Modem 7:

    Connection established - Select options:

    That indicates that the modems were communication and ready to negotiate bit rate. I selected T for Terminal mode and pressed Enter a few times. HyperTerminal displayed }{}}}}{}}{}}}{} . That indicates that bit rate negotation was not successful.

    This is an example of the problem as I understand it. The 14.4k modem at Grex answers the phone and tries to negotiate with a smart modem. The PMMI is not smart enough to negotiate with modems faster than 1200 BPS. I think only old 1200 BPS modems might work.

    Here is a quote from from Rich Cini in Thread: Bulletin board and Modem question

    "The only comment I'll make with regards to modems is that the auto-negotiation feature of the new modems (even 1200 baud modems) messes up the PMMI (and probably other 300-only baud modems). I found that I could only successfully connect to the 300-baud host if I forced the 1200-baud modem to work at 300-baud (on Windows, use a 300 baud port speed)."

    This makes the connection sound possible, but only if the host is expecting my call or uses a PMMI. When I get BYE running, Smart modems can call me if they set their terminal program to 600/450/300/110 baud. I'm using the PMMI because I like it and it already is on MITS format diskette. I'll upload smart modem software after I get a direct 9600 Baud connection set up.


  2. Default

    I have a Remote CP/M running using a PMMI modem, Vector Graphic board set, and 54K Vector Graphic CP/M.

    Does anyone have a modem, phone line, and time to call my system to test a file transfer over Vonage VoIP? If so, please send me a private message to get the phone number and arrange a test.


  3. #13


    Sorry to chime in a bit late on this thread - I've been on holidays.

    Re "I tried PIP and could not find support for a serial port. Thanks for the pointer to IMP. "

    Getting PIP to work is a bit tricky. CP/M may well have already mapped the serial port(s) to internal CP/M devices such as Reader and List. I did some quick research on the Altair and it depends on which computer you have, but I see some have DIP switches for the serial ports.

    A lot of my work uses the Altair SIMH so I'm familiar with the port settings for that and it may be they are similar - eg between 10H and 20H.

    I'm working on packet software at the moment using MP/M as a router, but one of the parts of this project is to interface to a machine that has virtually nothing on it. Build it up with PIP as Chuck says, pip over xmodem, recompile xmodem for the machine's port settings etc. You need some background information for that.

    As a testbed I'll be starting with a CP/M board with PIP and maybe Mbasic and not much else. It is a bit of an intellectual challenge to try to build it up from there, with ideally the smarts on the controlling machine.

    At the very minimum I'm thinking maybe Mbasic and OUT and IN commands, or PIP using existing devices and let CP/M do the work.

    I don't think the first program you PIP is xmodem though, as xmodem needs port settings to be known, and they will be different for every machine. I think the first program to PIP over is some sort of sniffer program that tests all serial ports and then the MPM board uses that information to build a custom version of xmodem, compiles it and sends it over. Then use xmodem to send over a terminal program that can talk to the packet network.

    What does the hardware look like on the back - is there a serial port anywhere?

    And what sort of software do you have? Any chance of Mbasic - if so then you could write a little program to send a byte to ports 0 to 255. On an Altair, I'd hope for some action from port 10H up.

    Alternatively, DDT may be useful to get the bios jump at 0005H and see where it goes and see where the ports are for the bdos calls for the reader and list devices. Do you have DDT?

  4. Angry

    Hello Dr_Acula,

    I was hoping to hear from you. It's not too late. Several people similar interests, but work in different years. I'm documenting what I find in web pages for the person next year.

    My test bed is very different. I'm not starting with a bare system. I'm upgrading what I have and will work my way backwards to early Altairs, non-MITs drives, and no hardware drives. I've quit using the PMMI modem for now and also waiting to implement "AT" command set modems. I'm doing parallel development using the Altair 88-2SIO and Vector Graphic Bitstreamer II. For now, I am ignoring the Altair 88-SIOA and non-MITS boards often used by early Altairs.

    I've made a lot of progress. I have the BSTAM communications software on both VG and MITS hard-sectored format. I have a Bitstreamer and MITS 88-2SIO boards in a VG configuration system and a MITS 300/25 configuration. I used BSTAM to transfer BYE, MEX, Modem7, Kermit, Sweep, and Wash to Altair format. PIP is out of the picture for now. I can also Squeeze/Unsqueeze files and use LBR libraries.

    I have a PMMI BYE working for 54K VG and 60K MITS CP/M 2.2. I want to upgrade my RCP/M to a newer version, eliminate modems, and use an RS-232 connection to an Ethernet serial server. I'm updating utilities too.

    The goal is a common set of tools with source code for 8251A/9551 IO, M6850 IP, standard MITS and VG addresses, VG CP/M, MITS Burcon CP/M, and Tarbell SSSD CP/M. I want a RCP/M a file transfer without Telnet. I'm using a GW312 serial to Ethernet server. Is anyone else using a serial to Ethernet device compatible with Tactical Software virtual COM drivers?

    I have a sub-domain that address my router and the firewall routes serial server traffic to two RS-232 ports. I can do console operation and file transfer without Telnet. Now I want to configure BYE and Xmodem.

    I don't remember the difference between BYE or MBYE. I'm looking for a recommendation and pointer to the best/latest source code for a RCP/M. I have BYE 7.2 for a starting point. I'll want MDM 7.?? and XMODEM source too.

    I'm not finding much code for the M6850 in MITS boards. The 8251A code uses software Baud rate selection, the Bitstreamer uses switches. I'm using CP/M MBASIC4 an Altair BASIC to initialize and test the M6850.

    I'd appreciate any advice on source code versions and source, BYE RCP/M without a modem, and Ethernet to serial connections. I'm currently researching 88-2SIO configuration and ready to learn what signals BYE needs to work without a modem.

    The back of my Altair has six 25-pin connectors:

    Three connectors are VG standard Bitstreamer ports A, B, and C. - Ignore for now

    One connector is a MITS Turnkey Module M6850 at 14H/15H for MITS BSTAM. Later, the port will be useful for an APE modem program.

    The last two connectors are for the MITS 88-2SIO console a modem ports. The MITS console only uses transmit, receive, and ground. The second port configuration is mostly undefined for MITS software. I think the default MITS handshaking and internal cable connections need some refinement.

    My next tests are an Altair 8800 to 8800b RS-232 link from Albuquerque to Denver. Does anyone have an RCP/M system on the internet?

    Tom Sanderson

  5. #15


    That sounds very interesting. I'm not an expert in this but I have some things that will be useful to you and some of the things you are doing look very interesting.

    About 12 months ago we had a N8VEM up for a week or two using a MSS100 serial to ethernet device. I've still got those ready to go and have the router configured for a fixed IP address, but the N8VEM was using a ram disk (448k) and it didn't have many files, plus it was possible to crash it remotely and then it needed rebooting. So I've had to go back to a more stable system, and that little project has taken a year.

    However, MPM on the propeller is looking more stable now, plus it is possible to host around 50mb of files on an sd card. So I'm almost back to where I was last year. I'd love to have something up permanently - and also maybe make it "crash proof". It would be great to do a link-up.

    Re xmodem, yes I have a source. Just need to patch three variables - input port, output port and input status port. Maybe patch the bit that changes when a byte is available on the input. I checked your link but not sure where the port addresses are.

    Re "I can do console operation and file transfer without Telnet " - ie do you mean raw bytes in and out?

    I need to find out more about these BBS programs. Could they do file transfer? My vague understanding of BBS programs were they run under an operating system and made the OS crash proof. eg on an OS you could upload a program and run it and it might be a program that just did a mindless loop and to the outside world the computer was broken. With a BBS that would be hard to do, right?

    I'm not sure about sources but I think there are others here who can help.

  6. Default

    >Re "I can do console operation and file transfer without Telnet " - ie do you mean raw >bytes in and out?

    I'm using proprietary drivers that make virtual COM ports on Windows PC. The drivers have a TCP/IP connection to a remote serial to Ethernet server. The server is connected to the Altair console port.

    I recently discovered that a PC terminal program can connect to the server with a standard TCP/IP connection.The standard TCP/IP connection had some character set problems, but could function as a Altair console without using the virtual COM port drivers or Telnet.

    IPCOMserver can use the virtual COM ports to implement a Telnet server. I see little reason to use Telnet.

    >I need to find out more about these BBS programs. Could they do file transfer? My vague understanding of BBS programs were they run under an operating system and made the OS crash proof. eg on an OS you could upload a program and run it and it might be a program that just did a mindless loop and to the outside world the computer was broken. With a BBS that would be hard to do, right?

    I used some early BBS systems, but mostly visited RCP/M systems. Later, I used TBBS on PCs. I suggest you make you questions operating system specific.

    CBBS was likely the first CP/M BBS. I don't remember much except that it had a lot of ASM code. I got a diskette from Ward, but was intimidated by ASM. I still have the diskette.

    Next, I looked at RBBS. RBBS was written in Microsoft BASIC and could be compiled by the Microsoft BASIC compiler. I don't remember what function was in RBBS. I do remember that compiling a large BASIC system was work on a small diskette development system.

    At this point my interest forked away from the BBS culture. I think a CP/M BBS might have a menu based file transfer option. My model was to use mini-RBBS. I had only minimum BBS message function. I also maintained a much smaller BASIC project.

    The RCP/M BYE program would load and run the mini-RBBS. That provided welcome instructions, user communication, and logging. The assumption was that the caller would exit the message system to do file transfer and command line operations.

    Think of my mini-RBBS as an remote only e-mail client.
    BYE was desktop sharing.
    XMODEM.COM was file transfer server.
    Modem was file transfer client.

    Modem 7 and MDM7xx were menu driven file transfer clients that included command line and utility program function as menu items. The file transfer clients became terminal programs that could transfer files using a RCP/M command line utility or a BBS File Transfer Area.

    The BBS became the user interface for users not wanting to work at the command line. The RCP/M was mainly for developers to distribute and update source code. The BBS interface evolved more social and less technical.

    The XMODEM.COM and Modem 7?? interaction was like cutting and pasting between shared desktops. A BBS was Facebook or a support forum.

    A BBS or RCP/M was not crash proof. Loss of phone connection might trigger a reset. A constant voltage transfer would prevent many crashes on systems with a linear power supply. The clock board might need battery backup and a trickle charger.

    The BYE program did protect from BDOS errors when callers selected a non-existant drive. A crashed system or a system in a loop would need a manual reset. Other options might be using a telephone answering machine remote control tone or an RS-232 signal for triggering a reset.


    Altair 88-22SIO
    88-2SIO to GW312 External Cable Cable

  7. #17


    Fast forward six years to 2016 and I (virtualaltair) have an Altair RCP/M running. I (virtualaltair) lost my login information an re-registered as altairSYSOP.

    The PMMI modem remains one of my favorite S-100 boards, however the internet and decline of the POTS telephone network make it less valuable. The PMMI modem is historically important, but there are now issues with speed negotiation and VOIP codecs. One land line is expensive considering the number of people with only a cell phone. A second land line was useful in the past and would be useful now.

    RCP/M software exists for "AT" command set modems. I took the approach of using a "dumb" RS-232 connection without a modem. Mike Douglas modified BYE 2.74 to use a MITS Altair 88-2SIO port 2 with CTS enabled. The Altair RS-232 port connects to a GW312 Serial Ethernet server. The GW312 can connect using Virtual COM Ports or Telnet. Telnet is currently in use because it does not require installing virtual COM drivers

    BYE 2.74 and XMODEM 4.7 combine to form a simple RCP/M with MINI-RBBS installed. The RCP/M may be the Last RCP/M running. The Altair RCPM is running on an Altair Clone and a real Altair mainframe.

    The RCP/M welcomes callers and requests help upgrading BYE.COM and XMODEM.COM plus adding IMP/KMD, MDM740, and XMODEM software.

    Telnet: for the RCP/M. Use MAIL.COM for MINI-RBBS messages.


  8. #18

    Default RCP/M RCP/M

    Remote CP/M System running on Altair 8800 and/or Altair Clone. New system just getting started (Dec. 2016) using circa 1981 CP/M software. File transfer with XMODEM.COM and simple BBS using MINIRBBS. Run A:MAIL for message system.



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