View source for BDV11 Bus Terminator/ROM

[[Image:BDV11.jpg|thumb|300px|right|BDV11 board]]

The '''BDV11 Bus Terminator/ROM''' board is a [[QBUS]] board that includes:

* [[bus]] [[terminator|termination]]
* [[bootstrap]]/[[diagnostic]] [[Read-only memory|ROM]]
* [[KW11-L Line Time Clock]] functionality

Physically, it is a [[DEC card form factor|quad]] board, the '''M8012'''.

The board is normally supplied with 2KW of PROM containing diagnostic and bootstrap functionality, with an optional 2KW for more; there are also sockets available for an additional 18KW of user-supplied [[EPROM]]. This memory does not appear directly on the QBUS; a 256 word window, and a window control [[register]], allows the entire contents to be seen.

In addition, the board provides a pair of [[DIP switch]]es (readable under program control, except for one used for KW11-L functionality control); and also a set of red [[Light Emitting Diode|LEDs]], a 'power OK' green LED, on-board RESET and HALT/ENABLE switches, and test points for on-board voltages. All of the latter are on the card edge, so they are accessible when it is plugged in. A single read/write [[register]] is provided for diagnostic purposes.

==KW11-L functionality==

The KW11-L functionality is enabled by switch E21-5. When on (closed), when the register is ''clear'', the bus BEVNT line is held low, preventing timer interrupts. Setting the 'interrupt enable' bit allows timer interrupts to happen. The KW11-L 'monitor' function and bit are not provided.

===KW11-L issue===

'''''NOTE''''': Once the KW11-L on a BDV11 has been enabled, RESET/etc do '''not''' disable it, unlike every other device in the [[PDP-11]] universe! (This is apparently because they were short a QBUS receiver for the BINIT bus line, and didn't want to add another complete chip to be able to monitor it.)

So if you start some [[operating system]] which enables the KW11-L (e.g. [[UNIX]]), and then try and re-boot it by halting the machine and using the 'Go' command to [[QBUS CPU ODT|ODT]], you'll probably get a clock [[interrupt]] in the process of booting, which will trash it.

The ''only'' thing that clears it is either a manual disable (write 0 to the KW11-L's CSR); something which toggles the BDCOK bus line - e.g. using the BDV11's on-board RESTART switch, or a front-panel restart switch; or power cycling the machine.

'''Caveat haquur!'''

==Board layout error==

There is a layout error on the BDV11 which can cause damage if a BDV11 is plugged into a system with the optional -12V on pin AB2. The [[trace]] which is supposed to connect bus line BIRQ6, on pin AB1, to the pullup network is incorrectly routed to pin AB2. The [[Engineering Change Order|ECO]] to repair this (DEC #2 for the BDV11) is fairly simple:

* Cut the trace (on the solder side) between E1 pin 11 and AB2
* Add a wire (on the component side) between E1 pin 11 and AB1

==Bus termination upgrade==

The BDV11 only provides termination for a Q18 QBUS; there is a relatively easy official DEC ECO (#5) to extend it to Q22, since there are 4 spare [[resistor]] networks available in one of the resistor packs. It is:

* Add a wire from BC1 (BDAL18) to E1 pin 15
* Add a wire from BD1 (BDAL19) to E1 pin 14
* Add a wire from BE1 (BDAL20) to E1 pin 13
* Add a wire from BF1 (BDAL21) to E1 pin 12

==Further reading==
	
* ''Location of W13 on the BDV11'', [[MicroNote]] #057

==External links==

* [http://www.bitsavers.org/pdf/dec/qbus/Digital_Microcomputer_Interfaces_Handbook_1980.pdf microcomputer interfaces handbook] - BDV11 is covered on pp. 86-113, 94-121 of the PDF
* [http://www.bitsavers.org/pdf/dec/qbus/Digital_Microcomputer_Products_Handbook_1985.pdf Microcomputer Products Handbook] - the BDV11 is covered in Appendix C (pp. 593-600 of the PDF)
* [http://www.bitsavers.org/pdf/dec/qbus/EK-BDV11-TM-001_Mar78.pdf BDV11 bus terminator, bootstrap, and diagnostic ROM technical manual] (EK-BDV11-TM-001)
* [http://www.bitsavers.org/pdf/dec/qbus/MP00489_BDV11_Sep77.pdf BDV11-A Field Maintenance Print Set] (MP00489)
<!-- * [http://bitsavers.org/pdf/dec/qbus/MP00740_1123_schem_Oct81.pdf PDP-11/23 Field Maintenance Print Set] (MP00740) - BDV11-A Field Maintenance Print Set (MP00489) is on pp. 16-31 of the PDF -->
* [https://avitech.com.au/?page_id=3407 BDV11 Upgrade]

[[Category: QBUS ROMs]]