16 Nov
2012
16 Nov
'12
7:10 p.m.
On 11/16/2012 06:59 PM, ben wrote:
4.77mhz is about as fast as 2901s will run without pipelining.
I did an 8/16 bitter with 2901Cs and was profoundly disappointed.
Add length like 20 or 36bits makes for problems like devices like disks
as most available will be 8 or 16bits. Then again with large disks
half word splits will fit. Makes it troublesome to do 12 or other odd by
current standards lengths for words.
As to PC killer, that was never needed, the pc was killing itself with a
cpu that
was 8080 with a bag on the side. I always felt that the 8086/88 was a
market successful while failed design. Maybe why I used PDP11s and Z80s
till 1991 when 32bits made the scene at least interesting. The PC was an
appliance, not the latest computing tech.
Allison
On 11/16/2012 4:14 PM, allison wrote:
Go two sided for ground plane and easier layout. the cost difference is
small.
Leds make crappy diodes and are very slow (large die). Leds are slower
than transistors.
Building them in as state indicators on board for testing and
troubleshooting
has merit. However even small Leds eat power and are as costly as a
transistor.
I use 2N3904s a lot for switching and RF
applications and it's a good
all round device.
Typically when I buy them I get 100 at a time as I use them for Zeners
(base-emitter
reversed is about 7V), Varicaps (base-collector reverse biased), High
conductance diode
(base shorted to collector) and of course as a transistor. Generally I
pay about 3-4 cents
(US) for known vendor parts.
What I was wondering was how much it would cost today ( single sided
pcb )
and modern parts, compared with the original product. I wonder what
speed leds
work at, and use them for switching diodes. The advantage is a nice
visible
logic gate. Hmm, A blue transistor when on would be nice too!
Another device
that is newer than the old bipolar transistor days are
the MOSFETs
specifically those in the 2N7000 and similar class as switches. They
offer very low
on resistance and high noise margin with the gate turn on voltage in the
3-8 Volt range.
Any one using them in quantity would do well to create a go/no-go tester
for leakage
and gain as a project like that will consume a lot of transistors and
marginal ones are
a big nuisance.
For diode the 1n914 and the 1n4148 are good choices for DRTL style
logic.
I am planning at the momement using 2901's, a nice 10/20 bit computer.
20 address bits, 4.77 mhz clock , byte access bus, and front panel -
The PC* killer . :)
1976 ish era mini-computer, rather than micro-computer with a micro-chip.
(Of course if any wants to put this design in silcon, feel free to do
so) :)
Allison
Ben.
* At the moment a design with static memory, now for dynamic memory
refresh cycle
I would have to check if it will fit in the micro-code rom.