[N8VEM: 16915] My SBC v2 build...

[p***@public.gmane.org]

Gents,

Here are some photos (finally!) of my SBC V2 build. Please note that this is my
first N8VEM build, and also I wanted to make a fully CMOS version of this nice
board. Don't be too critical to my soldering skills, and the fact that the board
is still not cleaned from the flux :D.

The Z80 SBC in its full glory:
http://postimg.org/image/pme2qvwp9/
http://postimg.org/image/57d022o99/

EPROM ZIF socket, mounted higher on 2 additional machined sockets, so it doesn't
interfere with the nearby jumpers:
http://postimg.org/image/dbppkk025/
http://postimg.org/image/bxy2p90st/
Link to Farnell: http://bg.farnell.com/aries/32-6554-11/socket-dil-zif-gold-32way/dp/1674708
In a normal build, I'll definitely use only a machined socket for the EPROM, not
the expensive ZIF. Also, the EPROM is without an opaque sticker on the quartz
window, because I expected to program it quite frequently in the beginning (you
know, searching for the right firmware version :D). I can fix this some day...

Z80 oscillator, 10 MHz, 5V CMOS:
http://postimg.org/image/5f58cbolp/
Link to Farnell: http://bg.farnell.com/vishay-dale/xo52ctelna10m/crystal-oscillator-10mhz-thd/dp/4666320
I looked for even faster DIP version of Z80, but this was the fastest one. Never
mind, it still has all the needed brain power for a homebrew machine.

UART oscillator, 1.8432 MHz, 5V CMOS, soldered "dead-bug" style:
http://postimg.org/image/mjdcnihql/
http://postimg.org/image/z5scy39l9/
Link to Farnell: http://bg.farnell.com/citizen-finetech-miyota/csx750fcc1-8432m-ut/oscillator-1-8432mhz-smd/dp/1838934
I still soldered the DIP8 socket on the other side, just in case.

DS1210 is replaced with wires between pins 1-8, 5-6:
http://postimg.org/image/ueshg2gr1/
I decided to not implement this part of the circuit, because it doesn't provide
any data safety. When writing a data structure is interrupted by power-down,
the structure will be left in inconsistent state. Even when writing a single
byte to the SRAM, the power can drop in the middle of a write sequence and
violate the SRAM timing specs, which can have unpredictable results. This is my
personal understanding and decision, feel free to do it your own way.

Homemade RR1 & RR2 resistor packs from SMDs:
http://postimg.org/image/c80zuuq19/
http://postimg.org/image/ynsm4huml/

UART connection to my FTDI USB-serial (note the resistive divider which
translates TXD 5V->3.3V so it doesn't fry the FTDI)
http://postimg.org/image/86oi2xn4d/
Looks like 16550 works OK with 3.3V CMOS levels on RXD, so I left it this way.
The reason why I didn't installed the MAX232 is that I'm currently using the
same FTDI USB-serial for all the ARM & FPGA boards on my desk, and was just
easier for me to use low-voltage serial. If I build the board as stand-alone
equipment, I'll definitely add MAX232 and industry-standard 9-pin connector.

Some close-ups photos of the main ICs:
http://postimg.org/image/nqrafq7v1/
http://postimg.org/image/z1yjhu43x/
http://postimg.org/image/ja3iusj0t/
http://postimg.org/image/f28qm1hl9/

And finally, these are my treasures (my collection of N8VEM boards):
http://postimg.org/image/uz2x50klp/

An interesting fact is that the board works without any issues on both 5V and
3.3V at 10 MHz, and the power consumption is ***@5V and ***@3.3V (this is
on-par with lots of modern MCUs like PICs & AVRs). One thing which I found out
was that my CMOS ECB bus buffers are a little bit different from the TTL ones
(their inputs doesn't have hysteresis, which can be an issue when talking with a
noisy ECB bus). I still haven't tested this theory, because I need to complete
at least 1 other ECB board.

My board uses 1MB EPROM, 512KB SRAM, with 32KB "window", configured in the
following way (I'm listing only the installed & used jumpers):
K1: 1-2 (A17_ROM is enabled)
K6: 1-2 (A18_ROM is enabled)
K7: 1-2 (A17_RAM is enabled)
K8: 1-2 (A19_ROM is enabled)
K10: 1-2 (CFG1_Q0 is connected to U16A)
K11: 1-2 (VCC is connected to U3D)
K12: 1-2 (Enable local INT signal from UART)

The SW version is RomWBW v2.5.1 from 25.June.2013.

Next steps: I want to finish my IDE & SDCARD boards and play with them. Then I
want to work on a fast (not bit-banged) SPI interface for the Z80, so I can
attach even more cool peripherals, like Gameduino (vintage sprite fun anyone?),
ethernet controller, wifi, zigbee, even hardware mp3 decoder...

This is for now. Happy holidays,
picmaster

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