Announcement

Collapse

Forum Rules and Etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.


Rule 1: Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.


Rule 2: Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.



Rule 3: Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.


Rule 4: "PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.


Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Rule 5: Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.


Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.


New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.


Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

processor "speed" ratings, specifications

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    processor "speed" ratings, specifications

    I have been spending some time modifying the TRS-80 model 100 to run at 2x clock IE 4.9152MHz.
    The production 80C85 specification clearly does not support such operation.
    And yet, it works well, under some conditions
    * you need to use fast RAM
    * you need to use fast ROM
    .. and here fast means <200nsec. I use 120nsec SRAM and 150 nsec EPROM.


    It occurs to me that, if one were writing specs for a processor, that they must have assumed something about the responsiveness of memory.
    If Intel assumed "typical or slow" memory, then that would clearly reduce max speed, whereas in the timing budget they could assume that memory was fast, perhaps that supports a higher clock rate.

    Is there some rule of thumb around this? What do processor vendors assume about memory speed when they are rating their devices?

    I've been experimenting with different speed ratings on processors too. It is clear that processors with faster ratings can sustain higher speeds (As expected) but they all seem to run a fair bit faster than their ratings suggest.

    thx

    #2
    Originally posted by Twospruces View Post
    It occurs to me that, if one were writing specs for a processor, that they must have assumed something about the responsiveness of memory.
    If Intel assumed "typical or slow" memory, then that would clearly reduce max speed, whereas in the timing budget they could assume that memory was fast, perhaps that supports a higher clock rate.

    Is there some rule of thumb around this? What do processor vendors assume about memory speed when they are rating their devices?
    When writing specs for a processor, the processor vendor just needs to publish detailed timing specifications as a function of the processor clock cycle period. Then it is the responsibility of the system designer to choose other system components with timing specification that are fast enough to meet the processor timing specifications at the desired processor clock cycle period.

    For example this OKI databook has timing specifications for the 5MHz rated MSM80C85A-2
    http://www.bitsavers.org/components/..._Data_Book.pdf

    Page 61 (page 66 of the PDF) has a table of A.C. Characteristics. Page 62 has a Bus Timing Specification as a Tcyc Dependent table. Page 63 has timing diagrams for Read and Write Operations with visual representations of the various timing parameters.

    Comment


      #3
      thanks. yes I have looked at it (alot) and I guess my impression is the specs they publish don't answer the "what if" scenario. meaning, for example, if RAM was significantly faster than the minimum requirement, can that support an increase in clock rate.

      The specs say - for the fastest clock I specify, memory has to be at least this fast. as dictated by the various worst case timings that the processor must see.
      The other way to look at it is - with the fastest ram possible what is the minimum clock cycle supportable?

      And yes I know there is a 5MHz rates 80C85. Interestingly it was measured to be no faster than the stock 3MHz rated part. IE they both tolerated about the same overclocked rate.

      There is also an 8MHz rated Tundra 80C85. That one has materially faster performance.

      In my testing, I had a crude clock synthesizer set up to drive clock rates in steps, so I could ratchet up the clock rate and measure when the device "hit the wall". It was pretty easy to tell when the processor started to see errored memory read/writes.

      Comment

      Working...
      X