On 8/18/2015 11:33 AM, Johnny Billquist wrote: > On 2015-08-18 15:09, Jay Jaeger wrote: >> On 8/18/2015 7:46 AM, Paul Koning wrote: >>> >>>> On Aug 17, 2015, at 10:48 PM, Jay Jaeger <[email protected]> wrote: >>>> >>>> BR level is the bus request level for an Interrupt. BR 4 is typical. >>> >>> On Unibus machines, more of the BR levels were used. The rule of >>> thumb was BR4 for slow devices (like terminals and printers), BR5 for >>> fast devices (disks and tapes), BR6 for real time critical devices >>> (clock, also DECtape because you had to respond to a “read block >>> number” interrupt fast enough to start reading the block before it >>> passed over the heads). BR7 could in theory be used by devices but I >>> don’t believe it ever was in practice. >>> >>> paul >>> >> >> Yes, but this discussion regards an RLV11. > > It was possible to use several BR levels on a Qbus as well, but in > practice it was not done. > > And I suspect the diagnostics wants to know so that they can set the PSW > correctly on interrupts. Just using the default number should be good > enough in the common case. > > Johnny
Yes, but from what I could tell from its manual, the RLV11 could ONLY use BR4 - had no jumpers to do anything else - it was designed in the days of the LSI bus, the QBus precursor, which only had the one signal. JRJ
