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Thread: How to test M8655 serial board

  1. #1

    Default How to test M8655 serial board

    Hi,

    I'm trying to test the M8655 board but I canīt make it send any character. This is my configuration:

    Code:
    Jumpers:
    FIL - open
    TTY - open
    SWD - closed
    W2  - closed (9600 baud)
    W5  - open
    
    SB  - open (no stop bit)
    NP  - open (no parity)
    EVN - open (even parity)
    NB1 - open (8 bits per char)
    NB2 - open
    
    Dipswitches:
           76543210
    XMIT - 11100100 (9600 baud, addr 04)
    RCV  - 11100011 (9600 baud, addr 03)
    
    Conections:
    BERG | DB9
    -----------
    F    | 2
    J    | 3
    VV   | 5
    
    BERG pin E to pin M
    
    Test program (loop that prints char "A"):
    0000 7200 CLA
    0001 7001 IAC
    0002 7002 BSW
    0003 7001 IAC
    0004 6046 TLS
    0005 5004 JMP 0004
    I think the TLS instruction uses the two numbers in the middle as the transmit address of the card, but even if I change them I get nothing. I tried putting a scope in the F pin of the BERG connector but the signal never changes. I guess I must be doing something wrong because I tried 4 different boards and none of them seem to work. I'm using a PC with a serial port and hyper terminal as a dumb terminal. Any ideas?

    Thanks!

  2. #2
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    Default

    That test program never waits for the character to print before going around the loop again. You need something like this:

    Code:
    0000	7200			CLA	/ INIT CHAR
    0001	6046		L1,	TLS	/ PRINT CHAR
    0002	6041		L2,	TSF	/ WAIT UNTIL PRINTED
    0003	5002			 JMP L2	/ SPIN
    0004	7001			IAC	/ INCRE CHAR
    0005	5001			JMP L1	/ LOOP
    Or if you want a simple read/echo program:

    Code:
    0000	6032			KCC	/ CLEAR FLAG
    0001	6031		L1,	KSF	/ SKIP IF CHAR
    0002	5001			 JMP L1	/ SPIN
    0003	6036			KRB	/ READ CHAR
    0004	6046			TLS	/ PRINT CHAR
    0005	6041		L2,	TSF	/ WAIT UNTIL PRINTED
    0006	5005			 JMP L2	/ SPIN
    0007	5001			JMP L1	/ LOOP

  3. #3

  4. #4

    Default

    Ok, so its necessary to loop until the char is printed even if I have a HALT instruction right after the TLS? because I tried this program and it didn't work either.

    Code:
    7470/ 7200	CLA clear AC
    7471/ 7001	IAC increment AC - now contains 0001
    7472/ 7002	BSW byte swap AC - now contains 0100
    7473/ 7001	IAC increment AC - now contains 0101 (65 dec)
    7474/ 6046	TLS transmit AC via UART
    7475/ 7402	HLT halt
    That program is for the M8650 board so, I'm not sure if it works for the M8655.

  5. #5
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
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    Default

    Assuming the hardware is set-up OK, the HLT should have permitted the character to have been transmitted.

    There must be something wrong with the configuration of the card or the power supply rails. The transmitter requires + and - 15V to be present.

    Incidentally, you have either 1 or 2 stop bits - never none!

    If you have an oscilloscope, you should be able to monitor the transmit decode 8251 IC (E40 pin 2?). It should operate each time you perform an IOT command on the transmitter.

    Dave
    Last edited by daver2; August 11th, 2019 at 01:22 PM.

  6. #6

    Default

    Quote Originally Posted by NicolasF View Post
    Hi,


    76543210
    XMIT - 11100100 (9600 baud, addr 04)
    RCV - 11100011 (9600 baud, addr 03)
    DIP switch RCV 6 is the 150 Ohm resistor.

    From Dough Jones site: ...As a special case, if the R=150 switch is on, the receive baud rate is set to 150 baud...

    I think this has to be off:
    Also I dont have the third switches on I think it should be:

    XMIT - 10000100 (9600 baud, addr 04)
    RCV - 11000011 (9600 baud, addr 03)


    Attached is a (very bad) picture of the switches of two working cards with 2400Baud (that is XMIT 10000100, RCV 10000011 from top to bottom).

    greetings
    Volker
    Attached Images Attached Images

  7. #7

    Default

    Quote Originally Posted by gnupublic View Post
    DIP switch RCV 6 is the 150 Ohm resistor.

    From Dough Jones site: ...As a special case, if the R=150 switch is on, the receive baud rate is set to 150 baud...

    I think this has to be off:
    Also I dont have the third switches on I think it should be:

    XMIT - 10000100 (9600 baud, addr 04)
    RCV - 11000011 (9600 baud, addr 03)


    Attached is a (very bad) picture of the switches of two working cards with 2400Baud (that is XMIT 10000100, RCV 10000011 from top to bottom).

    greetings
    Volker
    You are right, I had the switches wrong. Your combination worked. I also had other issues like one of the M8655 board were broken, and for some reason Iīm not able to run any program from bank zero, I have to use bank 1, also I measured the voltages on the omnibus and I'm not getting the +15V, instead I have +4.8V is this ok?

    Thanks!

  8. #8
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
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    Default

    The switch settings should only affect the BAUDRATE. You stated that you monitored pin F of the BERG connector but saw nothing. This is the transmit line itself, so should have had some activity even if the BAUDRATE switches were set incorrectly.

    The RS232 drivers will be using the +15V supply, so if it is down at +4.8V I would strongly urge you to investigate why before any damage results...

    It may be the power supply itself, or it may be a smoothing capacitor (e.g. C62 on the serial board itself).

    Dave

  9. #9

    Default

    How about the handshake wires?
    Dwight

  10. #10

    Default

    Quote Originally Posted by daver2 View Post
    The RS232 drivers will be using the +15V supply, so if it is down at +4.8V I would strongly urge you to investigate why before any damage results...

    It may be the power supply itself, or it may be a smoothing capacitor (e.g. C62 on the serial board itself).

    Dave
    Dave has a point.

    I guess that this is the same PDP-8E as the TU56 belongs to. If you haven't payed any attention to the power supply, stop doing anything more! Start with the power supply in the computer and in the TU56 before you doing anything else. Bad power supplies can cause a lot of strange behaviors and even destroy things.

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