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I recently updated the Z80 Membership Card CPU card to rev.B, and the
Front Panel card to rev.D. No big changes; but here are the improvements:

CPU rev.B

The 5v regulator U8 has been flipped upside down, so its metal tab faces
up (away from the board) instead of down (against the board). This
improves its ability to dissipate heat if you're running with an
unregulated 6-9vdc supply.

I added a 6-pin power/serial connector P4. Its pinouts are the same as
P4 on on the Front Panel, so a Sparkfun 5v USB-serial cable #9718 plugs
right in. This connector is located in the same place as U8; so install
one or the other (not both). If you are getting 5v power from the
USB-serial cable, then you don't need the U8 regulator.

P3 was added to jumper the serial input to the Z80 /INT input. This
connection was made on the Front Panel; but with the P3 jumper, you can
use the CPU board all by itself (no front panel). Use a serial terminal
to talk to the monitor or run BASIC or other programs.

Options were added to jumper bus P2 pin 28 to HALT or /BUSAK, and bus P2
pin 29 to /NMI or BUSRQ. This provides access to these pins if needed
for your own accessory cards.

Front Panel rev.D

I replaced the hard-to-find LED-photoresistor coupler with a standard
LED-phototransistor coupler. This required a new pulllup resistor, R2D.

The optocouplers I bought seem to have a little too much gain. Some
users have found that they can still hear the piezo when it should be
off. My hearing isn't good enought to tell! If you hear it, try a lower
value pullup for R2D, or replace the optocoupler with a lower-gain part.

Forward into the past,
Lee Hart

--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com