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Z80 Single-board computer (with AVR controller)

Another Z80 single-board computer.

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Another Z80 single-board computer.
Like a lot of other folks these days, I grew up in the early IC microprocessor era. My first computer at age 14 was a MICROACE kit, which was the SINCLAIR ZX-80 before SINCLAIR bought the design and sold it. I quickly expanded it to 8KB of RAM and replaced the "membrane" keypad with a HEATHKIT full-size "leaf-spring" keyboard that I found at a local hamfest.

This is my Z80 SBC design with a few "modern day" enhancements, such as PJRC TEENSY 2.0++ being used as a "host" to facilitate the generation of various Z80 clock frequencies (8MHz, 4MHz, 2MHz, 1MHz, etc), loading of programs directly in RAM (i.e. "boot code" for CP/M), emulation of a "virtual UART", emulation of a "virtual disk drive" (using an SD memory card), etc.

Wait_State_Generator-8Mhz-0ws_Live.pdf

Programmable wait-state generator, logic analyzer capture, 8MHz/0ws, M1 = 240nS

Adobe Portable Document Format - 12.59 kB - 10/20/2016 at 21:37

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Wait_State_Generator-8Mhz-7ws_Live.pdf

Programmable wait-state generator, logic analyzer capture, 8MHz/7ws, M1 = 1120nS

Adobe Portable Document Format - 13.29 kB - 10/20/2016 at 21:37

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Wait_State_Generator.jed

Programmable wait-state generator, JEDEC file

jed - 4.42 kB - 10/20/2016 at 21:36

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WSGEN-1V00.si

Programmable wait-state generator, logic equations

- 2.67 kB - 10/20/2016 at 22:07

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WSGen-1v00.PLD

Programmable wait-state generator, simulation input

- 3.16 kB - 10/20/2016 at 22:12

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Discussions

Adam Vadala-Roth wrote 01/24/2017 at 21:48 point

your wiring job reminds me of building an oscilloscope on a breadboard for an embedded systems class using a ARM7 on a DIP PCB lol 

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esot.eric wrote 01/24/2017 at 07:42 point

Cool project. I gotta admit, though, I feel like your method for posting updates, here, doesn't lend itself well to others' commenting on your project.

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Scott wrote 01/24/2017 at 15:32 point

Hi Eric:

Thanks for visiting and thanks for the complement.  Comments can be added on the other site and do not require a user log-in to do so.  Also, one can "follow" the updates to the project page by clicking on the "follow" button on the upper-right hand corner of all the posts,


If HACKADAY-IO's editor was a bit more project-meister-friendly for blog entries then I would keep everything here but alas, the editor allows no flexibility, 

Peace and blessings.

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Scott wrote 01/24/2017 at 06:08 point

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Scott wrote 12/04/2016 at 09:49 point

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Scott wrote 11/22/2016 at 09:41 point

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Scott wrote 11/21/2016 at 17:05 point

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Scott wrote 11/19/2016 at 05:32 point

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Scott wrote 11/19/2016 at 05:31 point

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Scott wrote 11/18/2016 at 23:42 point

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Scott wrote 11/08/2016 at 08:21 point

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Scott wrote 10/23/2016 at 05:54 point

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Scott wrote 10/23/2016 at 05:54 point

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Scott wrote 10/23/2016 at 05:54 point

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Scott wrote 10/23/2016 at 05:53 point

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Scott wrote 10/23/2016 at 05:53 point

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Scott wrote 10/23/2016 at 05:52 point

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Scott wrote 10/23/2016 at 05:52 point

Seems I have to actually post in order to get notices out to followers.  Thanks for following. :)

Testing the AVR's interrupt latency: https://z80avrproject.wordpress.com/2016/10/10/103/

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Scott wrote 10/20/2016 at 04:28 point

Folks:

I have been posting  my progress on this project here: https://z80avrproject.wordpress.com/

It has a better editor than HACKADAY.IO and I seem to be able to add in-line photos as well.  Honestly, I am not thrilled with either site's editing features.

Peace and blessings,

Scott

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Scott wrote 10/09/2016 at 07:56 point

Sunday, October 9, 2016

I wired the 74HC299 onto a solderless bread-board along with my TEENSY 2.0++ running AttoBASIC V2.34 and a CD4511 driven 7-segment display connected to the outputs of the 74HC299.  AttoBASIC [http://cappels.org/dproj/AttoBasic_V2_Home/Atto_Basic_V2_Home.html] makes a great development platform to test interface and operation of various devices while evaluating them.  It beats repeated writing, debugging and downloading of code into the AVR.   Once again, I found it instrumental in accomplishing the task at hand.  Reading the datasheet can be a little confusing with regards to determining proper operation as a bidirectional parallel-to-serial and serial-to-parallel device.  Since I am out of full 8-bit I/O ports on the AT90USB1286, this seemed the way to go and it comes in a 20-pin DIP or a 20-pin SOIC package.  DIP for testing and SOIC on the PCB.  Using SPI "mode 2" and setting the OE's and S1 low achieved the output function on the first try.  After fiddling to find the right combinations of the states of S1 and OE, I was able to get my test code to work.

In short, the sequence is as follows:
  Sequence to read from the bus;
   1) Set S1=1 and OE=1
   2) Perform a dummy SPI write (toggles the CLK line to load the registers with the state of the I[7..0] pins)
   3) Set S1=0 to enable bit right shifting
   4) Read data from the bus with an SPI read
   5) Set S1=1 to end the bus read.

  Sequence to write data to the bus;
   1) Set S1=0 and OE=1 to enable bit right shifting
   2) Perform an SPI write with the desired data
   3) Set OE=0 to enable the output drivers
   4) Set S1=1 and OE=1 to end the bus write and tri-state the pin drivers.

The AttoBASIC test code is as follows:
  10 REM 74HC299 TEST
  15 SDC7; SBC7 # OE=1 -> HI-Z
  20 SBC6; SDC6 # (S0=1) S1=1 -> READ DATA
  25 SPM 2 # SPI TO MODE 2
  30 FOR N=0 15 # LOOP DIGIT TO DISPLAY
  35 GOSUB 55 # WRITE TO BUS
  40 GOSUB 65 # READ FROM BUS
  45 NEXT; SPS # CONTINUE LOOP
  50 END # END PROGRAM
  55 CBC6; CBC7; PRI "N="; PRI N; SPW N # S1=0 -> SHIFT RIGHT OE=0 -> OUT TO BUS
  60 SLP4; SBC6; SBC7; RETURN # WAIT, S1=1, OE=1 THEN RETURN
  65 SPW 0; CBC6; PRI "DATA: "; PRX SPR; SBC6; RETURN #DUMMY WRITE, S1=0, PRINT BUS DATA, S1=1 THEN RETURN

Time spent was less than an hour.

Next up; determine if the AVR can emulate an 82C55A PIO.

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