N8VEM Single Board Computer Home Page

 

Welcome to the N8VEM Single Board Computer Home Page

 

The N8VEM Single Board Computer is a home brew Z80 small computer project. It is made in the style of vintage computers of the mid to late 1970's and early 1980's using a mix of classic and modern technologies.

 

Designed with the free KiCad EDA toolset. PCB routing provided by FreeRouting.net  All software is developed in Z80/8085 assembler using the following toolset for MSDOS called Telemark Cross Assembler (a.k.a. TASM)  A major design goal is to use freely available tools to the maximum extent possible.  You can help out too!  See the help wanted section below.  The PCB design is supplemented using component libraries available here KiCad Libraries, specifically the Zilog Z80 CPU and Intel 8255 PPI chips.

 

Encourages low cost development and assembly by hobbyist amateurs using common tools such as 25 watt soldering iron, VOM, logic probe (optional), and common hand tools.  An oscilloscope is recommended but not required.  Some basic electronic skills are good but the PCB is designed for relative beginners.

 

Design principles include using low cost commonly available standard TTL DIP components such as 74LSxxx using 0.1" spaced through hole technology.  Design avoids usage of advanced PCB construction techniques such as SMT and custom and/or hard to obtain components.  Also avoids usage of programmable devices such as PALs, GALs, CPLDs, and FPGAs except for standard EPROM components.

 

Computer is designed to be a low cost Single Board Computer with simple IO.  The current design supports a UART for serial IO and PPI for parallel IO.  Includes RTC for time keeping with battery back up and a small amount of NVRAM storage.  While low cost is a key goal, the SBC is also designed to be a component in a larger bus based system. The SBC includes an ECB connector. 

 

Current description of the SBC is:

Z80 CPU 4MHz

512K SRAM

1M EPROM

16C550 UART with connector

82C55 PPI with connector

DS1302 RTC with battery backup with small amount of NVRAM

ECB buffers, logic, and connector

Standard PC drive connector power supply interface, +5V only

Reset key with external connector

Power LED

Boots to RAM based debug monitor

CP/M 2.2 available at monitor prompt

A: drive is 32K ROM (10K is system tracks)

B: drive is 448K RAM (64K of 512K SRAM is dedicated system memory)

F: drive is 992K ROM (32K is system track)

 

 

 

 

Useful links:

 

http://www.vintage-computer.com/vcforum/

 

http://www.vintage-computer.com/vcforum/archive/index.php/t-10499.html

 

http://groups.google.com/group/comp.os.cpm/topics?lnk=lr

 

http://www.classiccmp.org/mailman/listinfo/cctalk

 

http://unicornelectronics.com/ (parts are available at any electronic part supplier.  This is not intended to be an endorsement of any but are just examples)

 

http://www.jameco.com  

 

http://www.bgmicro.com

 

http://www.midwestsurplus.net/en-us/front.html

(this is a small electronics surplus store near where I live.  If you'd like to support a small business with your purchase, here it is.  I have purchased most of my parts from here.) 

 

Help needed:

 

1. write MSDOS program to create ROM images in CP/M Disk Parameter Block (DPB) format for the ROM drive. (Juha working on this. Please see discussion area)

 

2. clean up all the source files

3. replace TASM301 with free (as in speech, similar license as KiCad) licence

4. build and test new PCB when available (done, PCBs have been ordered, ETA first week of June)

 

5. test alternative parts to reduce cost. In particular, 128Kx8 27C1001 EPROMs and 128Kx8 SRAM and 512K x 8 FLASH ROM.  (anyone have a 128Kx8 0.6" 32 pin DIP SRAM they can lend me?)

 

6. edit this webpage to look decent

 

7. Redo KiCad schematic as hierarchical sheets

8. Convert serial IO routines to interrupt driven from polling (or post a Z80 8250/16550 interrupt assembler example)