VCB01 VCB01

[Carl Lowenstein]

In article <10461 at eddie.MIT.EDU> nessus at athena.MIT.EDU (Doug Alan) writes:
>I know that it is possible to connect two VCB02's (GPX QDSS video
>display controllers) to a VAXstation II, but I have never seen anyone
>connect two VCB01's (normal QVSS video display controllers).  Does
>anyone know if this is possible, and if so, do you know how to
>determine the CSR address of the 2nd VCB01?

VCB01's have two sets of addresses to worry about:  the display memory
and the control registers.

The standard setup puts the 1/4 megabyte display memory starting at
Q-bus address 017000000, which is the top of the 22-bit Q-bus space.
This gets mapped to microVax address space starting at 0x3ffc0000.
The (64-byte) register space is normally based at Q-bus I/O page address
017777200, which is mapped to microVax address space 0x20001e80.

There are switches on the board which select different addresses.
Address bits <21:18> of the display memory start can be changed, thus
moving it about in 1/4 megabyte address steps.  Address bits <12:06>
of the control register base can be changed, in 64-byte steps.

Caveat:  "To take advantage of certain MicroVax architectural features
when programming bit-map operations, the video memory always resides
in the topmost 256 Kbytes of the I/O physical address space."

Information from VAXstation II Technical Manual AZ-GLFB-MN (1985).



-- 
	carl lowenstein		marine physical lab	u.c. san diego
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	cdl at mplvax.ucsd.edu	cdl at mplvax.nosc.mil