Hi Peter The TM section (4.11) on the read-write register looks to me like a comprehensive descrioption of it's functionality; esp if read with an LS299 data sheet. There may be second order points which study of the maintenance (schematic) prints will reveal - but I would be surprised, this is intened to be vanilla. The (useful) student guide you identified gives a good precis of R/W register function on page BD-15ff. The R/W register looks like a 16 bit register, writable at byte granularity for testing / exercising minimal systems. Very useful for low level diagnostics / faultfinding of DATI DATO DATOB bus cycles. HtH; Martin -----Original Message----- From: Peter Ekstrom via cctalk &lt;cctalk(a)classiccmp.org&gt; Sent: 23 November 2025 16:52 To: General Discussion: On-Topic and Off-Topic Posts &lt;cctalk(a)classiccmp.org&gt; Cc: Peter Ekstrom &lt;epekstrom(a)gmail.com&gt; Subject: [cctalk] Re: BDV11 programming information Hi Glen, Yes, and I have looked over it several times. It does have quite a bit of info, but it doesn't go into much detail for the R/W register. I also found a student guide that includes the BDV11 and it help shed some light on how the code in the ROMs is segmented. It helped me visualize more how it is done. But I am still missing things like the details for the R/W register. https://wwcm.synology.me/pdf/EY-DX056-SP-002&J6269-A&EY-DX052-SG-00… - Peter On Sun, Nov 23, 2025 at 10:52 AM Glen Slick via cctalk < cctalk(a)classiccmp.org&gt; wrote:

Hi Peter There are also the maintenance drawings http://www.bitsavers.org/pdf/dec/qbus/MP00489_BDV11_Sep77.pdf ... Note that there are two 256 byte (128 word) windows High and Low, both defined by the PCR, Table 4-3 of the Technical Manual presents a concise appreciation. I should think that peek / poke will confirm the ROM windowing logic, and both the TM and Training Manual contain (terse) information. The documentation looks complete to me, no need to start with a beeper and draw the schematic. However, it is arguably abstruse - the target audience being systems folk. Best Regards Martin From: Peter Ekstrom &lt;epekstrom(a)gmail.com&gt; Sent: 27 November 2025 16:48 To: Martin Bishop &lt;mjd.bishop(a)emeritus-solutions.com&gt; Cc: General Discussion: On-Topic and Off-Topic Posts &lt;cctalk(a)classiccmp.org&gt; Subject: Re: [cctalk] Re: BDV11 programming information Hi Martin, I see what you are saying. I guess I was hoping for some more details documented somewhere. The disassembled ROM file has helped shed more details on the whole paging method for code to appear in the 256-byte window. I'll keep tinkering. Thanks, - Peter On Mon, Nov 24, 2025 at 6:44 AM Martin Bishop <mjd.bishop@emeritus-solutions.com<mailto:mjd.bishop@emeritus-solutions.com>> wrote: Hi Peter The TM section (4.11) on the read-write register looks to me like a comprehensive descrioption of it's functionality; esp if read with an LS299 data sheet. There may be second order points which study of the maintenance (schematic) prints will reveal - but I would be surprised, this is intened to be vanilla. The (useful) student guide you identified gives a good precis of R/W register function on page BD-15ff. The R/W register looks like a 16 bit register, writable at byte granularity for testing / exercising minimal systems. Very useful for low level diagnostics / faultfinding of DATI DATO DATOB bus cycles. HtH; Martin -----Original Message----- From: Peter Ekstrom via cctalk <cctalk@classiccmp.org<mailto:cctalk@classiccmp.org>> Sent: 23 November 2025 16:52 To: General Discussion: On-Topic and Off-Topic Posts <cctalk@classiccmp.org<mailto:cctalk@classiccmp.org>> Cc: Peter Ekstrom <epekstrom@gmail.com<mailto:epekstrom@gmail.com>> Subject: [cctalk] Re: BDV11 programming information Hi Glen, Yes, and I have looked over it several times. It does have quite a bit of info, but it doesn't go into much detail for the R/W register. I also found a student guide that includes the BDV11 and it help shed some light on how the code in the ROMs is segmented. It helped me visualize more how it is done. But I am still missing things like the details for the R/W register. https://wwcm.synology.me/pdf/EY-DX056-SP-002&J6269-A&EY-DX052-SG-00… - Peter On Sun, Nov 23, 2025 at 10:52 AM Glen Slick via cctalk < cctalk@classiccmp.org<mailto:cctalk@classiccmp.org>> wrote: