TU58 problems

tony duell ard at p850ug1.demon.co.uk
Sun Jan 17 08:19:55 CST 2016

> On a VAX, there is an application (named EXCHANGE if I remember
> correctly) which reads and writes the first partition of any RT-11 disk

Err, yes... This implies I have a working VAX. Until I repair ths TU58 and get
it to load the CPU microcode, I don't.


> If you have a PDP-11 system with a serial DL port, don't forget that
> it must also be set at the same speed as the TU-58 tape drive.  While
> it seems unlikely that you have not made sure with the VAX and the
> TU-58 tape that they both have the same baud rate, check just in case.

Now I am confused.... I suspect it's 'near enough' but not spot on. The 
TU58 is running at 38400 baud, which I understand is correct for the
VAX11/730 internal drive. In any case it's the unit that was inside my VAX
CPU when I got it and there is no reason to assume the controller board 
was swapped out, The rate is set by wire-wrapped links on the TU58
controller board and those are right. I've also checked the frequency at
the clock pins of the UART chip.

But while the printset for the 11/730 CPU claims a 38400 baud rate clock
(acutally 16 times that at the input to the serial chip, of course), I can't for
the life of me work out how the 10MHz CPU clock oscillator is divided down
to give this. I get it running at around 39kbps. I guess as it's async it will 
work, but....

I do not think this is the problem. I am sure the VAX console processor and
the TU58 are communicating.


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