[Info-vax] DZQ11 on VAX/4000 Model 300

[John E. Malmberg]

On 1/14/2019 5:18 PM, Stephen Hoffman wrote:
> On 2019-01-14 22:41:35 +0000, David Wade said:
> 
>> That I understood. The board I added was a 4-port serial which I 
>> understood to be low priority. Therefore I placed it at the left hand 
>> side of the existing cards. It all worked.

You are lucky.  I do not put DZQ boards in production systems.  When 
properly working they use excessive CPU at any reasonable baud rates, 
and at high baud rates they can cause a machine check.

>> When I removed it it was the last card on the BUS so there were no gaps.

> The daisy chain—the DMA grant and related—is part of the mess here. The 
> CSR and vector addresses can and variously do change when the Q-Bus bus 
> is reconfigured.
> 
>> Given the limited config, as far as I can see the default settings for 
>> each card should be fine. However I will re-run CONFIGURE and see what 
>> it suggests for board configurations...
> 
> Some of these old beasts had a load board as the power supplies needed 
> enough of a power draw and an empty half-box was enough to fault out the 
> supplies, not that I've looked at a BA box in a very long while, and not 
> that I recall whether the BA440 was one of the backplanes that required 
> a load board when it was mostly-empty.   One obvious work-around was to 
> use a few grant cards and to move some random Q-Bus board over into the 
> other half of the backplane, if there wasn't a load board handy.

I had that happen on a BA440 system that was upgraded from a VAX-3xxx to 
a VAX 4000 Model 50.  That removed most of the Q-BUS options.  With out 
a q-bus load board, the system would not properly power up.

Given how easy it is to machine check a VAX 3xxx or VAX 4xxx system with 
a single active DZQ serial port, and how much more load it puts on the 
system instead of a CXYxx serial port, the one use I could see for that 
widget is to use it as a load.  Just make sure no one ever tries to use 
any of the serial ports.

> But CONFIGURE is your friend, any time you make any changes to the Q-bus.
I would have to go find the documentation, and I do not remember if the 
KZQSA has a floating vector for the first unit.

Regards,
-John