23 May
2000
23 May
'00
7:50 a.m.
This is what I meant exactly - no bi-directional data bus. I'm guessing that
there is a fine distinction between dual-ported and separate input and
output busses...
Rich
==========================
Richard A. Cini, Jr.
Congress Financial Corporation
1133 Avenue of the Americas
30th Floor
New York, NY 10036
(212) 545-4402
(212) 840-6259 (facsimile)
-----Original Message-----
From: Dwight Elvey [mailto:elvey@hal.com]
Sent: Monday, May 22, 2000 9:27 PM
To: classiccmp(a)classiccmp.org
Subject: Re[2]: Altair parts substitutions
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
In any case, the 5101 is (AFAIK) just a single-ported 256*4 CMOS RAM.
It's not a dual-ported device.
Hi
No, it is not dual ported but it has separate
input and output ports and not a bidi bus.
Dwight
23 May
23 May
11:40 a.m.
On Tue, May 23, 2000 at 08:50:52AM -0400, Cini, Richard wrote:
This is what I meant exactly - no bi-directional data
bus. I'm guessing that
there is a fine distinction between dual-ported and separate input and
output busses...
Um, it's a *big* difference! Dual-ported means two separate ports that you
can use at the same time. Separate in/out just means no need to disable
the chip's drivers when writing to the memory. Faking separate I/O using
bidir parts plus external buffers is easy. Faking DP using regular RAMs is
a bigger deal, you need some kind of arbitration and something to generate
mem cycle timing 2+ times as fast as the two busses that are attached. Still
could be cheaper than truly dual-ported memory though, especially if you need
something big but not too fast.
John Wilson
D Bit
4:45 p.m.
This is what I meant exactly - no bi-directional data
bus. I'm guessing that
there is a fine distinction between dual-ported and separate input and
output busses...
Specifically, a true dual-ported RAM chip has separate address busses and
control signals/strobes (*RD and *WR, or *CS and R/*W, or the like) for
each port.
Dual-port RAM chips tend to be expensive and not very high-density, so
they aren't commonly found in commodity computer hardware. It's usually
more cost-effective to time-multiplex a single port.
Current manufacturers of dual-port RAM chips include Cypress and IDT.
There are even some quad-port RAM chips now.
7:17 p.m.
Eric Smith <eric(a)brouhaha.com> wrote:
Most of the dual ported RAM chips that I know of were used
on video boards. These had parallel I/O on one side and
serial I/O on the other.
In the microprocessor designs we do, we designate the RAMs
as follows:
1RW Single port/ may have separate in and out busses
1R1W Dual port. Separate addressing for read and write
5R5W Multiport. A real pain to test {:-0>
We do use quite a few multiported RAM as internal design
but it would be hard to use these as single chips.
Dwight
This is what I
meant exactly - no bi-directional data bus. I'm guessing that
there is a fine distinction between dual-ported and separate input and
output busses...
Specifically, a true dual-ported RAM chip has separate address busses and
control signals/strobes (*RD and *WR, or *CS and R/*W, or the like) for
each port.
Dual-port RAM chips tend to be expensive and not very high-density, so
they aren't commonly found in commodity computer hardware. It's usually
more cost-effective to time-multiplex a single port.
Current manufacturers of dual-port RAM chips include Cypress and IDT.
There are even some quad-port RAM chips now.
8992
days inactive
8992
days old
3 comments
4 participants
participants (4)
-
elvey＠hal.com -
eric＠brouhaha.com -
RCini＠congressfinancial.com -
wilson＠dbit.dbit.com