8085 project

Discussion in 'Homework Help' started by Razvannn, Apr 17, 2012.

  1. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    I have to make a 8085 based project in a PCB design program (altium design, eagle, proteus, doesnt mind that much).
    I need to use:
    -an 8085 microprocessor
    -32kB SRAM
    -8kB SRAM
    -16kB EPROM
    -8251
    -HCT 573
    -1 paralel port 8212

    The problem I have is how do I connect the pins. I dont know how to distribuite the memory correctly and how to use those parts.
     
    Last edited: Apr 17, 2012
  2. MrChips

    Moderator

    Oct 2, 2009
    12,453
    3,371
    You need to learn about microcomputer system bus.
    For SRAM and EPROM you have to select part numbers.
    In an expanded system you will need a 16-bit address bus and an 8-bit data bus.
    Since the data is multiplexed with the low address, you will need an 8-bit address latch.
    You will also need address decoders to select your RAM, ROM and devices.
     
  3. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    yes I know a few about the components I have. I looked out for the pinout of each. I know how 8085 works.
    I found CD54HCT573 latch, KM62256C for sram 32kB, AS6C6264 8kB sram
     
  4. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    Nice to see 8085 uP...
    But believe me its no so simple to build 8085 Board, and the level you want is very very hard!

    Here is the link of my 8085 SBC which use to SOD testing it has work for few time after changing the delay, after that i have no energy too mess with it, but i will like to work with it again in vacation!
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,453
    3,371
    Ok, then the next step is to start drawing a schematic and connect all the components.
    Don't even bother with a CAD program. Start connecting the parts with pencil and paper.
     
  6. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    Last edited: Apr 18, 2012
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    If you use the 3 bits for adress decoding. You will have 13 bits for adressing. Or 8 pages of memory with 8K bytes each. So without complicating things to much. You should perhaps look for 8K x 8 Static RAM/ROM chips. The selection of those kind of chips are quite good.
     
  8. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    I must use the chips I wrote in the first post. I need to use a 16k EPROM and one 32k and one 8k SRAM.


    How do I use 8251 and what is it for ? To which components do I connect it ?
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,453
    3,371
    Why not Google 8251 and find out?

    Remember, this is your Homework, not for us to do the work for you.
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    No it really do not matter if you use several 8K RAM/ROM chips. The address space will from the CPU be seen as continuous if you do things correct. If your teacher do not say you have to use those chips. It will be much more easy to use 8K units. But if you want to be stubborn be my guest. I guess my at lest 15 years of experience with controllers do not matter much in your book. Which grade is this project for. In any educational setting you would not get such a project. Without taking some course first. To learn the basics. But to me it looks like you somehow miss the technical knowledge needed to do such a project
     
  11. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    As for the components, this is a "theoretical" project. I have to use the components I've been given.
    @t06afre - I do understand what you are saying but I can't do it that way (im not allowed to).
     
  12. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    I thought a one line long hint would help me a lot.
    I've been searching about the serial transmitter but can't relate very much to what i have to do.
     
  13. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    I made another scheme in paint in which i connect 573 hct latch.

    http://s17.postimage.org/yys8slpwd/hct573a.jpg

    is this correct ?

    I think I found out how to connect 8251:
    With 16-bit adress buss I can acces 64k memory, from which only 56 is ocuppied. So the decoder 74LS158 has 8 outputs and are connected this way :
    01 - 16k EPROM
    2345 - 32k SRAM
    6 - 8k SRAM
    and 7 - points to 8251 ?

    scheme for the 74LS158 : http://postimage.org/image/w8o8q3pol/
     
    Last edited: Apr 18, 2012
  14. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    You could do some research on how the IO/M pin (34) is used together with the in and out instructions
     
  15. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    thanks. so the IO/M connects to enabler of the decoder so when M is selected the decoder for memory is enabled, right ?
     
  16. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    yes that is correct. But in your system. You can also have what is named memory-mapped IO. Then A15 to A13 is 1. No memory will be selected. And hence you can use the rest of the address bus to address the UART and PIO. It is up to you as a designer to select how to do it. Both methods are correct
     
    Razvannn likes this.
  17. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    It is something with your adress decoding that to me looks very wrong. I do not think your setup will work at all. I think you must decode as follows.
    As long as pin 34 (IO/M) is low
    If A15 is 1 the 32K RAM is selected.
    If A15 is 0 and A14 is 0 the EEPROM is select
    if A15 is 0 and A14 is 1 the 8K RAM is selected.
    The PIO and UART has to be mapped as IO device and only active as long IO/M is high using the lower part of the address bus for decoding.
     
    Last edited: Apr 19, 2012
  18. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    so what you are saying should look like this right ?

    http://s15.postimage.org/3rij47wzd/mem2.jpg

    What to do with the 8k space ? put the connection to 8251 there ?
     
  19. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    I think it is better it is better to use a 74ls139 for decoding. Connect the A15 to the A1 input and A14 to A0. Then connect Y2 and Y3 to an XNOR gate (74ls266). I leave it to you to find out how to connect the ROM/RAM further. Also remember the IO/M pin. Somehow this must be connected to the t4ls139 maybe via some extra logic. That will be up to you to decide. You will also have an extra decoder in the 74ls139 chip. Perhaps this can be used for decoding in the IO space.
     
    Razvannn likes this.
  20. Razvannn

    Thread Starter New Member

    Apr 17, 2012
    10
    0

    thx for the tip; i will work on it;
     
Loading...