Qbus split I&D?

Don North ak6dn at mindspring.com
Mon Mar 16 23:23:50 CDT 2015

On 3/16/2015 8:42 PM, Eric Smith wrote:
> On Mon, Mar 16, 2015 at 9:10 PM, Christian Gauger-Cosgrove
> <captainkirk359 at gmail.com> wrote:
>> Unfortunately, the cost of MRAM chips is rather a lot, especially
>> since you can't just order small batches. Minimum order on Mouser was
>> 128 chips at something like $20 CAD per.
> Digi-key sells them without any minimum order quantity. Their quantity
> 1 price for the 1Mx16 35ns TSOP-54 device (p/n MR4A16BYS35) is $36.72.
> Not including parity or ECC, it takes two devices to fill the entire
> 4MB address space of the PDP-11/70. Either parity or ECC will require
> another one additional device, which won't be fully utilized.
> Ordinary SRAM is cheaper, but $110.16 for enough RAM chips to max out
> a PDP-11/70 doesn't seem all that expensive, unless you're comparing
> to DDR SDRAM DIMMs for PCs.

Most any FPGA development / evaluation boards for the major devices from A and X
come with onboard DDR SDRAM that is typically from 16MB to 64MB, so in that case
the memory is more or less free.

If one were to build a state of the art FPGA board from scratch even then adding a
couple of dollars worth of DDR memory is no big deal (one or two devices) given the
fact that most of the mid/higher end FPGA devices have hard macro DDR controllers
in them these days.

The Terasic Cyclone IV based board comes with 32MB of SDRAM memory, an EP4CE22
Cyclone IV device with ~600Kb of internal memory and ~22K logic elements. It can be
had for about $80 these days. It is several year old tech at this point.

The BeMicroCV board comes with 128MB DDR3 memory, a 5CEFA2 Cyclone V device
with ~1700Kb of internal memory and ~25K logic elements. It can be had for only $49.
See: https://parts.arrow.com/item/detail/arrow-development-tools/bemicrocv#zgRz

For the X vs A folks there are a number of similar boards available at Digilent, 
altho they
tend to be a bit higher priced and a few more bells and whistles (lights and 
switches) etc.

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